WASHINGTON (AP) -- Federal health officials warned Internet users Wednesday to beware of a concoction made of apricot seeds that's touted as a cancer cure, as a Florida court case became the government's latest attempt to quell a resurgence of laetrile.

In the 1970s, thousands of patients went to Mexico seeking laetrile, and some doctors sold it in the United States, before a National Cancer Institute study concluded the substance did not fight cancer. Experts also warned that laetrile pills could cause cyanide poisoning.

So the Food and Drug Administration declared laetrile illegal. Several states fought the FDA action but courts backed the government, ending laetrile's heyday by 1980.

Now laetrile is rebounding on the Internet, sometimes sold under the aliases amygdalin or "vitamin B17."

Wednesday, the FDA announced that a U.S. District judge in Miami had issued a preliminary injunction halting sales by three Internet sites, and warned consumers to beware.

"We do not want people to take products that have not been proven to be safe and effective," said FDA enforcement chief John Taylor, saying the biggest worry is that patients will forego proven cancer therapy.

The judge's ruling temporarily stops laetrile sales by World Without Cancer Inc. and Health World International Inc., of Bay Harbor Fla., and Arizona-based Health Genesis Corp., which also does business in Bay Harbor Island, while the court considers an FDA lawsuit seeking to permanently halt the sales. The FDA said since 1998 its inspectors have warned David E. Arjona, a official of all three companies, that laetrile is illegal, yet those inspectors bought laetrile from his Web site in June.

Arjona did not return a phone call. His attorney, Kirkpatrick Dilling of Chicago, was not aware of the preliminary injunction but said his client "hasn't sold one thing that's harmful to anybody."

The Florida case is the FDA's third laetrile crackdown this year, part of the agency's new attempt to block Internet sales of unapproved drugs. In April, a federal judge ordered a New York company to stop selling laetrile -- in July, a federal grand jury indicted an Ohio laetrile seller.

Copyright 2000 The Associated Press.