After reviewing scientific approaches to HIV vaccine development, this article discusses problems in testing the vaccines. The problems include the obtaining of reliable evaluations of candidate vaccines under existing regulations, vaccine developers' fears of liability for adverse reactions to vaccines, the cost-effectiveness of extensive animal trials, and the designing of clinical trials to demonstrate whether the vaccine tested is safe and effective. The scientific and ethical issues attending the testing of candidate vaccines are complicated by uncertainty about the potential liability for adverse reactions to any vaccine. The public interest in having an HIV vaccine available promptly is likely to outweigh any interest in holding manufacturers accountable for injury by means of strict liability. The task for public policy is to develop ways to ensure a safe and effective vaccine supply while providing for the care of those who may be adversely affected by the vaccine. A comprehensive system of public and private health insurance and disability income assistance could eliminate the need for most persons adversely affected by the vaccine to seek compensation through the tort system. 65 references.