The scientist at M.D. Anderson Cancer Center in Houston was hardly discreet. “Here is the bones … of what you want,” he wrote to researchers in China.

Attached was a confidential research proposal, administrators said. The scientist had access to the document only because he had been asked to review it for the National Institutes of Health — and the center had examined his e-mail because federal officials had asked them to.

The NIH and the FBI have begun a vast effort to root out scientists who they say are stealing biomedical research from institutions across the U.S. Almost all of the incidents involve scientists of Chinese descent, including naturalized U.S. citizens.

Seventy-one institutions are investigating 180 cases involving potential theft of intellectual property. So far, the NIH has referred 24 cases in which there may be evidence of criminal activity to the inspector general’s office of the Department of Health and Human Services.

“It seems to be hitting every discipline in biomedical research,” said Dr. Michael Lauer, deputy director for extramural research at the NIH.

The alleged theft involves scientific ideas, designs, devices, data and methods that may lead to profitable new treatments or diagnostic tools.

Some researchers under investigation have obtained patents in China on work funded by the U.S. government and owned by U.S. institutions, the NIH said. Others are suspected of setting up labs in China that duplicated U.S. research, officials said.

Roughly a dozen scientists are known to have resigned or been fired from U.S. universities and research centers so far. In several cases, scientists supported by federal agencies are accused of accepting funding from Beijing in violation of NIH rules. Some have said that they did not know the arrangements had to be disclosed or were forbidden.

In August, Feng Tao, 48, a chemist at the University of Kansas, was accused of failing to disclose an appointment at a Chinese university while receiving federal funds.

His lawyer, Peter R. Zeidenberg, suggested that prosecutors were targeting academics who had made simple mistakes. “Professors, they get their summers off,” he said. “Oftentimes they will take appointments in China for the summer. They don’t believe they have to report that.”

The investigations have left Chinese and Chinese American academics feeling “that they will be targeted,” said Frank Wu, a law professor at the University of California Hastings School of the Law. Critics note that the Justice Department had to drop charges against at least four Chinese American scientists since 2014: two former Eli Lilly scientists, a National Weather Service hydrologist and a professor at Temple University.

But officials said the investigations have uncovered clear evidence of wrongdoing. In one case at M.D. Anderson, a scientist with a suitcase packed with hard drives containing research data was stopped at the airport on the way to China, Lauer said.

Overall, they argued, the cases paint a disturbing picture of economic espionage in which the Chinese government has been taking advantage of the U.S. biomedical research system built on the free exchange of ideas.

Last month, married scientists, Yu Zhou, 49, and Li Chen, 46, who had worked at Nationwide Children’s Hospital in Columbus, Ohio, for a decade, were indicted on charges that they stole technology and used it to apply for Chinese patents and set up biotech companies. Zhou’s lawyer, Glenn Seiden, said the couple did not commit any crimes.

In May, Drs. Li Xiao-Jiang and Li Shihua were fired from Emory University after administrators discovered that Li Xiao-Jiang had received funding from China’s Thousand Talents Program. They had worked at Emory for more than two decades, researching Huntington’s disease.

“They treated us like criminals,” Li Xiao-Jiang said.

“Our work is for humanity,” Li Shihua added. “You can’t say if I worked in China, I’m not loyal to the U.S.”

The real question, Lauer said, is how to preserve the open exchange of ideas amid security concerns.

“The effects this will have on long-term, trusting relationships are hard for us to face,” McKinney said. “We just are not used to systematic cheating.”