Cerebrospinal fluid (CSF) was analysed in 170 AIDS patients. All of them showed HIV positive serological tests. All of them showed neurologic syndromes related to AIDS. The time period of the investigation was July 1984 - April 1989. In 8 cases (4.7%) CSF composition was normal. Lymphoma cells were observed in three cases. Aseptic meningites occurred in 34 cases (20.1%). Aetiological diagnosis of associated infection was established in 88 cases: cryptococcosis in 28 (35.9%); toxoplasmosis in 20 (25.6%); syphilis in 10; candidiasis in 3; Chagas disease in 2; tuberculosis in 1; nocardiosis in 1; schistosomiasis in 1. Antibodies for other virus were detected in 7. Bacteria were isolated in 5 cases. Anti-HIV antibodies were tested in CSF samples of 55 cases: they were found in 48 (87.3%). Two or more associated infections were observed in 15 cases. Changes of CBF composition in AIDS are discussed taking into account changes reported.