BALTIMORE -- A Johns Hopkins School of Medicine researcher violated federal regulations in a 2001 experiment that led to the death of a volunteer, the Food and Drug Administration has concluded.

In a March 31 warning letter, the FDA said Dr. Alkis Togias failed to apply to the agency before using the chemical hexamethonium bromide in research that led to the death of Ellen Roche in June 2001.

The letter, posted on the FDA's Web site Thursday, also said he failed to get the approval of a university oversight board before changing the experiment, and failed to properly warn volunteers of the study's risks.

FDA officials recommended that Togias' research be restricted, and ordered him to explain how he would begin complying with several regulations they said he violated.

Roche's death about a month after she inhaled hexamethonium bromide led the federal government to temporarily shut down most of Hopkins' research involving human subjects. Almost all the research -- but not Togias' -- was allowed to resume within six months of the shutdown.

Togias is negotiating a settlement with the FDA and his research has resumed, Johns Hopkins said in a statement. It did not describe what restrictions were being placed on his research.

"Dr. Togias has cooperated fully in all aspects of this matter and anticipates reaching an appropriate agreement with the FDA regarding research activities falling within that agency's jurisdiction," the statement said.

The statement did not say when Togias' research resumed or how many people are involved.

Messages seeking comment from Johns Hopkins, the FDA and Togias' lawyer were not immediately returned Friday afternoon.

Roche, a lab technician at Johns Hopkins' Asthma and Allergy Center, had taken part in an experiment designed to help scientists understand how the lungs of healthy people protect against asthma attacks. Her family reached a settlement with the school in 2001.