When the tiny advertising firm mono opened its doors in January 2004, it had the pending business of one client -- and a remodeled guest bedroom for an office.

Four years later, mono still has its first client -- "Sesame Street" -- plus a portfolio of household-name clients including General Mills, Hitachi, PBS, the Science Channel and USA Network.

It's been a gradual but steady rise in fortunes for the Minneapolis agency, one that once required a long plane and car ride to Jackson Center, Ohio, to land its second client: Airstream, the manufacturer of the iconic mobile homes.

"We've been pretty selective in the things we wanted to work on," said Jim Scott, mono co-founder and managing partner. "We wanted a national stage so when we call on people they know what we do, what we want. We said no to a couple of local clients."

Mono's gross billings have jumped from $2.2 million in 2004 to a projected $30.5 million this year. The staff has increased from the three founding partners to 23 employees. In the fall, mono will move from a cramped, renovated photo studio to a larger space on Hennepin Avenue in the Uptown district of Minneapolis.

But mono is not enamored of the notion that bigger is necessarily better. The firm likes the flexibility and intimacy that small provides. The name -- mono, with a lowercase m -- was selected to underscore the lack of bureaucratic layers in the agency.

The three founding partners came from large Minneapolis agencies. Scott was an account executive at Carmichael Lynch; Chris Lange and Michael Hart were creative directors at Fallon.

"At Fallon, we'd spend half of our time selling ideas internally. If we could reduce that step, we'd have more time to develop ideas and spend with clients," Hart said.

In the early days of the agency, Scott, Lange and Hart worked out of Lange's south Minneapolis home. Each took out a home equity loan and pooled resources to open a $15,000 checking account for expenses. A $50,000 line of credit was acquired (although it was never used), and the principals deferred salaries.

"We had a client, and that was comforting," Hart said.

Mono's first campaign for "Sesame Street" was called "Heroes," and was intended to remind viewers that the organization was about more than selling Bert and Ernie dolls. It featured childhood photos of such notable people as astronaut Neil Armstrong, former First Lady Eleanor Roosevelt, Olympian Wilma Rudolph and civil rights leader Martin Luther King Jr.

At the end of the spot were the words, "Every child is a story yet to be told. Over 35 years believing in the potential of every child. Sesame Street."

"It was not a huge client, but it gave us national brand and visibility," Hart said.

But mono's start-up wasn't without a few blips and stumbles. Some clients were unprepared for the firm's out-of-the box thinking.

"We spent hundreds of hours working with clients only to see great ideas die because the ideas pushed the envelope beyond what their respective categories considered traditional," Scott said.

While mono was developing the "Sesame Street" campaign, advertising holding company MDC Partners offered an investment in the fledgling agency. MDC's portfolio at the time included Crispin Porter + Bogusky, arguably one of the hottest agencies in the country then and now.

Chuck Porter, MDC's chief strategist and chairman of the Crispin agency, approached Scott about taking an equity stake in mono.

You gotta go where the talent is

"These guys had a great reel of material," Porter said. "Ultimately, clients gravitate to where the talent is. The fact that they wanted a lot of people to see their work, that was a pretty big thing."

Not wanting to lose control of the agency, mono initially demurred on the proposed investment. But eventually, the company agreed to give MDC a 49 percent share for an undisclosed price, keeping majority ownership in the hands of the three founding partners.

"It gave us working capital and financial stability," Scott said.

Not too long after that, the USA Network was looking for help with its brand, and selected mono over several other agencies. The cable channel had a wide variety of programing and was looking for an identity. It featured crime shows such as "Monk" and "Law & Order," sports, science fiction, comedy and movies.

Mono came up with the slogan "Characters Welcome," to emphasize a theme that strong personalities were part of each of the TV genres carried on the network.

"This was a defining arrival for us," Hart said. "We showed an ability to simplify complex brand problems."

Mono later came up with brands for the Science Channel -- "Question everything" -- and Public Radio International -- "Hear a different voice" -- as well as an eat-healthy campaign for General Mills and an infomercial for a new upscale oven called Turbochef.

"We're a branding agency rather than an advertising agency," Lange said.

Mono's newest client is Mrs. Meyer's Clean Day, a line of ecologically safe, scented cleaning products produced by the Minneapolis firm Caldrea, which also is the name of another line of "aromatherapeutic" home products.

Although Mrs. Meyer's products are available at 4,500 stores nationwide, this will be its first national advertising and branding effort.

The Mrs. Meyer's pitch will roll out in September in several test markets, said Michelle Sahlstrom, marketing director for Mrs. Meyer's.

"We've been courting mono for years," Sahlstrom said.

"Mono looks at things differently. They're not afraid to be irreverent or to turn something on its head. They're small but not from a small background. They're nimble creatively and really fast," she said. "I have very high expectations, and they have exceeded every one."

And then there was the call a year ago from someone from "Apple" that Scott fielded, thinking it was Apple Vacations or Apple Finance.

"Tell me about your company," Scott asked the caller. "Well," the Apple executive said, "We make the iPod."

Mono got the job with Apple, doing back-to-school and Christmas holiday work.

Scott laughs about that call now. "I take that as a sign that we're doing OK," he says.

David Phelps • 612-673-7269