From July 1986 through June 1990, 33,199 sera from various risk groups were collected in Veterans General Hospital-Taipei for detection of antibody against human immunodeficiency virus, type 1 (HIV-1). Sixty-five samples were proved positive by Western blot analysis. Among individual high risk groups, hemophiliacs had the highest positive rate of 20/60 (29.41%), followed by homosexual/bisexual males (41/1,264, 3.24%). The overall positive rate was 65/33,199 (0.19%). Ten cases were recognized as acquired immunodeficiency syndrome (AIDS), 1 case had AIDS-related complex (ARC) and 4 case had other apparently symptomatic infections. Among these 15 cases, 7 expired, 1 lost of follow-up and 7 surviving cases are being treated with zidovudine (AZT). Most of symptomatic HIV-1 antibody positive cases had abnormal T4/T8 ratio of 0.39 +/- 0.54 as compared with the asymptomatic HIV-1 carriers at a ratio of 0.81 +/- 0.69. The opportunistic infections included Pneumocystis carinii pneumonia (PCP) in 6 case, disseminated cytomegalovirus infection in 6 cases, herpes zoster virus infection in 3 case, candidiasis in 4 cases, syphilis in 3 cases, pulmonary tuberculosis in 2 cases, and others with cryptococcosis, salmonellosis, Mycobacterium avium-intracellulare infection, gonorrhea, Staphylococcus aureus endocarditis and bacterial sepsis, etc. The natural history of HIV-1 infection to AIDS involved acute and persistent multiple infections. Although prevalence of HIV-1 infection was low in Taiwan, nationwide surveillance of HIV-1 infection in various risk groups is still needed.