42 homosexual or bisexual men with persistent generalised lymphadenopathy not attributable to an identifiable cause have been followed longitudinally since February, 1981. Lymphadenopathy was accompanied by fatigue, low-grade fever and/or night sweats (57%), splenomegaly (29%), leucopenia (40%), hypergamma - globulinaemia (76%), and diminished proportion and absolute numbers of helper T cells (95%). Of the 26 patients who had lymph node biopsy, all showed benign reactive hyperplasia. After 15-30 (median 22) months, 8 patients have met criteria for the diagnosis of acquired immunodeficiency syndrome (AIDS). This outcome was associated with previous heavy nitrite inhalant use, with the presence of night sweats, with leucopenia, and with the triad of constitutional symptoms, splenomegaly, and leucopenia. In addition, a lower mean absolute helper T cell count and an increased frequency of anergy to mumps intradermal antigen and of herpes simplex virus isolation distinguished these patients from those remaining in the cohort, who seem to be stable and in some cases to have improved.