KIE: The French government has halted a program of clinical trials to test the potential antitumor properties of human interferon following the deaths of four patients from heart attacks. The deaths have helped spur a growing debate over whether it is ethical to permit human experimentation on such a large scale before more is known about the effectiveness and side effects of interferon. Concerns have also been expressed that hospitals may have been using unregistered batches of interferon in the government-sponsored trials.