In response to widespread concern about illegal drug use and the associated risk of the spread of HIV/AIDS, a study was undertaken to examine whether it was, in principle, feasible to conduct a trial providing heroin to dependent users in a controlled manner. Such a trial involves real ethical issues which are examined in this paper. The general issues examined are: should a trial be an experiment or an exercise in public policy?; acts and omissions; countermobilization; termination of a trial, (...) and payment for drugs and for a trial. The specific issues examined are: selection of trial participants; privacy; issues for staff working on a trial; coupling the trial with other treatment, and issues for researchers. A number of alternative approaches to the various ethical issues are presented and discussed. (shrink)