AIDS poses an even worse problem in developing countries than elsewhere because the counts of AIDS cases are accepted as gross underestimates, tracking of AIDS carriers is rare, government health resources are already stretched thin, and little is known about the cost-effectiveness of alternative approaches to prevention. No policy can be successful, argue the authors, in the current state of ignorance. They review what little is known, identify the cost-effectiveness questions that must be asked if the available resources are not to be wasted, and make recommendations about the kinds of information gathering and analysis that must be undertaken.