Geraldine and Donald Kidston were delighted when their son Barry enrolled in a chemistry class at George Washington University in 1976 and began doing experiments in the basement of the family's home in Bethesda.

"He worked on the top of my washing machine . . . and used my dishwasher to clean his flasks, tubes and dishes," recalled Geraldine Kidston.

Too late, the Kidstons discovered that their son was actually making drugs for his own consumption.

"He got into what is now known as designer drugs," said Geraldine Kidston, fighting unsuccessfully to hold back tears as she testified before a congressional hearing. Drugs first temporarily paralyzed her son, she said, later left him in a catatonic state drooling at the mouth and, finally, killed him in 1978 at the age of 24.

The Kidstons told their story yesterday at a hearing convened by the Senate Budget Committee to study the problem of "designer drugs," which experts define as legal substances produced privately from common chemicals. Drug laws are based on the molecular structure of drugs, so minor changes in the molecules of an illegal drug can create a new drug that is legal but produces a feeling of euphoria as powerful as heroin, according to experts at the hearing.

An estimated 100 people have been killed by "designer drugs" and a number of users have developed symptoms of Parkinson's disease, including paralysis and trembling, according to testimony. Almost all of those cases occurred in California.

Congress now is considering legislation to outlaw such drugs. Sen. Lawton Chiles (D-Fla.), ranking minority member on the Budget Committee and a cosponsor of one such bill, warned at yesterday's hearing that without such legislation, the "designer drug phenomenon could revolutionize the way drugs are used and sold in our country" because they are made "in clandestine laboratories by phantom chemists."

Chiles said the cost of manufacturing designer drugs is only a fraction of the cost of smuggling heroin or cocaine into this country and the profits potentially are much greater.

Gary Henderson, a pharmacologist at the University of California at Davis, who coined the term "designer drugs," testified that a handful of common chemicals can be designed to provide 200 million doses that can be sold on the streets as "China white heroin" for as much as $70 billion.

They are the drugs of the future, Henderson said.

"It doesn't make sense to import drugs from halfway around the world when you can make them for nothing in your own kitchen," he said.

Henderson said it is possible to buy the needed chemicals from chemical supply houses and mail-order firms. Handbooks telling how to assemble the needed equipment are equally accessible, he said.

Geraldine Kidston, accompanied at the hearing by Barry's father, a retired State Department official, said Barry bought a variety of chemistry books and visited Washington area libraries to learn more. At one point he went to the medical library at the National Institutes of Health, she said, to photocopy pages from books.

Eleven months after Barry enrolled in the chemistry class, he began to show the kind of symptoms that have come to be identified with "designer drug" use, his mother said.

"One day he was stiff, and he couldn't bring his arms down out of the air," she said. "He had to walk around with them stuck straight up."

The doctors who treated Barry that time diagnosed him as a catatonic schizophrenic and administered electric shock treatments, Kidston said. After the treatments were completed, Barry returned home and lived with his parents for about six months. In mid-1978 he moved into an apartment in Greenbelt.

That was where she found him on Sept. 3, 1978, slumped over, drooling and catatonic. Kidston took her son home, but he stayed only a short time before calling a friend to come and pick him up.

"I can still see Barry walking out the carport door -- a big grin and a wave goodbye," she said.

Kidston did not see her son alive again, she testified. On Sept. 7, 1978, he was found dead under a tree on the NIH campus. An autopsy listed the cause of death as a drug overdose.