Research on AIDS involving human subjects poses in stark form a familiar dilemma: Can the demands of a rigorous scientific research design be met without violating the rights or harming the interests of research subjects? The dilemma is especially troubling in the early phases of drug research, when promising medications showing some signs of success in combatting this fatal disease must be tested for safety and efficacy. The research design using randomized controlled trials, in which an experimental drug is tested against a placebo, highlights the dilemma. Although the use of this research design does not pose the only ethical problem for AIDS research, it is perhaps the most dramatic. Related ethical issues include the question of when an experimental drug that holds out the only present hope may be released for general use; who should be selected to receive experimental drugs that are in short supply; how much information should be released about safety and efficacy while a clinical trial is still in progress; and what factors determine the appropriateness of early termination of a study.