The measures taken by the National Government in 1991 against drug problems in Switzerland included new therapeutic experimentation; among others, it mentioned trials with diversified prescription of narcotics (including injectable heroin, morphine and methadone as well as smokable heroin and cocaine) to heroin-dependent persons with severe health and/or social problems. The number of persons receiving heroin is limited to 250, for a period not exceeding the end of 1996. The trials have to respond to scientific criteria of evaluation as well as to standards of comprehensive care. Research questions concern the feasibility, the efficacy and the cost effectiveness of trials in comparison with usual methadone maintenance programs. First trials started in Zurich, others are planned in Basle, Berne, Fribourg, Olten, Schaffhausen, Thun and Zug.