The relationship between cerebrospinal fluid (CSF) markers of HIV infection and the spectrum of neurological manifestations were studied in 15 AIDS patients (13 with and 2 without confirmed neurological disorders). We demonstrated the presence of intrathecally synthesized anti-HIV antibodies. Antibodies to HIV envelope proteins were present in all patients but those to HIV core proteins in 9/13 cases only. HIV antigen and HIV p24 antigen were present in 6/14 and 4/12 cases respectively. HIV was not isolated from 6 samples of CSF. We have demonstrated that CSF markers of HIV infection were present in all AIDS patients, with or without neurological manifestations. Moreover HIV p24 antigen seems to be a very reliable marker of HIV infection.