The government has approved human testing of an AIDS drug derived from cucumber roots that is the only agent shown to kill AIDS-infected cells selectively in the test tube, officials say.

The drug, GLQ223, is a highly purified version of an abortion drug used in China that is made from a type of cucumber tuber.Food and Drug Administration spokesman Brad Stone said his agency gave the drug's developers the go-ahead this week to start testing the compound in humans. The first stage of tests will only look at the drug's safety, not its effectiveness in fighting AIDS, Stone said.

The initial tests are expected to begin in May at San Francisco General Hospital, said officials at the University of California-San Francisco, which helped develop the drug.

Stone said GLQ223, whose unique promise has excited many AIDS researchers and activists, did not receive any special treatment.

"Like any AIDS drug, it got top priority and we were able to get it out of here (and into tests) in about two weeks," he said.