Research progress in the understanding of HIV and its effects on the human immune system continues at a rapid pace. Such research is yielding new ideas for chemotherapeutic agents, immunologic stimulators and modifiers, and potential vaccines. Clinical trials to test these approaches are under way. Despite the accomplishments, the epidemic progresses unchecked, resulting in continued suffering and death and enormous demands on the health care system of many nations. Clinicians have had to deal with new and difficult opportunistic infections. Yet advances in the treatment and prevention of these illnesses have benefited many AIDS victims. In the United States, the AIDS epidemic is now concentrating in the inner cities, involving injection drug users, minorities, heterosexuals, women and their offspring. In the developing world, AIDS continues to be predominantly a heterosexually transmitted disease, where more than one third of prostitutes in central African cities are infected. The major burden of the AIDS epidemic in the remainder of this and the next century will be in India and Southeast Asia, again predominantly via heterosexual spread. A great deal is now understood concerning the life cycle of HIV. More light has been shed on the interaction of HIV and CD4+ T cells, the cellular and viral factors involved in viral expression vs. latency, the function of the viral regulatory and structural proteins and the role of cytokines in regulation of HIV expression. Our understanding of the precise mechanisms whereby HIV causes a loss of CD4+ T cells remains incomplete. The direct infection and cell killing of CD4+ T cells is important and is supported by recent evidence demonstrating a high viral burden in these cells in the lymphoid tissue of patients. Over the last 1 to 2 years, there has been new evidence for indirect mechanisms of CD4+ T-cell depletion and/or dysfunction including: autoimmune reactions, perturbations of specific V beta T-cell receptor populations, infection of T-cell precursors in bone marrow and thymus, immunosuppression and dysregulation by viral proteins, possible super-antigen effects, and antigen-induced apoptosis or programmed cell death. New information has come forth in our understanding of B-cell abnormalities in HIV pathogenesis, including the putative role of IL-6 in B-cell activation and the identification of EBV in B-cell lymphomas in the CNS of patients with AIDS. It is expected that these and future discoveries concerning immunopathogenesis of HIV infection will help steer the therapeutic effort. Major strides continue to be made in the therapeutic arena for HIV infection and its complications.(ABSTRACT TRUNCATED AT 400 WORDS)