mid growing concern about the safety of medical research involving humans, the Department of Health and Human Services opened an investigation on Wednesday into a lead-paint study in Baltimore overseen by Johns Hopkins University.

The study was criticized last week in a decision by the Maryland Court of Appeals, which likened it to the infamous Tuskegee syphilis study decades ago.

The investigation by the department's Office for Human Research Protections comes just a month after a five-day suspension of federally financed medical research on humans at Johns Hopkins following the death of a healthy young volunteer in an asthma study on June 2.

The lead-paint study was conducted in the early 1990's to test how well different levels of repair in Baltimore rental housing worked to reduce lead in the blood of inner-city children.

Two mothers later filed negligence lawsuits against the Kennedy Krieger Institute, an affiliate of Johns Hopkins, saying that the research institute had failed to warn them about the risks of the study and the danger that their children could be poisoned by lead in the houses.

Last week, the Maryland Court of Appeals overturned lower court decisions dismissing those cases and sharply criticized the researchers and their institutions as failing to see the basic impermissibility of a study that enlisted healthy children to live in potentially dangerous housing.

"It can be argued that the researchers intended that the children be the canaries in the mines but never clearly told the parents," Judge Dale R. Cathell said in a scathing decision that compared the Baltimore study to Nazi medical experiments and the study in Tuskegee, Ala., that withheld treatment from black men with syphilis.

Neither researchers nor parents, Judge Cathell said, have the legal right to put healthy children into a study that offers them no benefit and carries real hazards. Children who ingest lead can suffer brain damage.

Dr, Gary Goldstein, the chief executive of Kennedy Krieger, defended the study and the institute's record in treating and preventing lead poisoning in the poor neighborhoods of Baltimore.

"We were not trying to put children in houses and watch them get lead-poisoned," Dr. Goldstein said. "We did not expect anyone to get lead-poisoned. The point was to show, in a neighborhood where 95 percent of the houses contain lead and 35 percent of the kids have lead poisoning, that with some repairs, you could move into a house like this and stay and not get lead-poisoned."

He added: "For the majority of kids in the study, lead levels did go down. To compare this to Tuskegee makes no sense."

Late on Wednesday, the Office for Human Research Protections sent a letter asking Johns Hopkins, which receives more federal money for medical research than any other university, to review the procedures used in the lead study.

Neither the agency's spokesman, Bill Hall, nor the Hopkins spokeswoman, Joann Rodgers, would provide details of the investigation.

Kennedy Krieger is an outpatient institute specializing in developmental disabilities. The procedures for its research projects are reviewed and approved by an institutional review board at Johns Hopkins, where its professional staff holds faculty appointments.

The study was designed to test lead levels in five groups of housing. The 75 homes in three of the groups received maintenance and repairs to reduce lead levels: 25 had minimal repairs, including scraping lead- based paint; 25 had a middle level of repairs; and 25 had extensive work, including replacement of windows and covering floors. The study also included two control groups, one of homes in which all lead hazards had been eliminated and the other of houses that never had lead paint.

For two years, the researchers took periodic blood, dust and water samples to measure contamination.

Kennedy Krieger helped landlords get public financing for eliminating lead and encouraged them to rent the premises to families with young children. Children already living in the houses were encouraged to remain, so that their blood could be analyzed.

"Through the repairs and cleaning, the homes in the study had 70 to 90 percent reduction in their lead levels, but all the families knew that lead was still a potential, because we gave them cleaning tips about what they should be doing to keep lead levels down," Dr. Goldstein said. "The impression of everyone doing the study was that everyone understood the situation."

But Suzanne Shapiro, the lawyer for Catina Higgins, one of the mothers who filed suit, said that was not the case. In May 1994, Ms. Shapiro said, when Ms. Higgins and her 4- year-old son, Myron, moved into a rented house at 1906 East Federal Street, the lead in Myron's blood was at a safe level and his mother knew nothing about the study.

"After she moved in, Kennedy Krieger enrolled her in the study, and she signed the informed consent, but no one ever told her, `There's lead in this house, and and it can cause brain damage,' " said Ms. Shapiro, who specializes in lead-poisoning cases and has other clients who participated in the study.

Ms. Shapiro said that a month later Myron's blood contained excessive lead, and that he had since had neurological problems.