We analysed 127 specimens of cerebrospinal fluid (CSF) from 118 HIV-1-infected individuals at different stages of infection. Intrathecal antibody synthesis was evident in 23 samples tested and was more frequently directed against HIV than against rubella virus, herpes simplex virus, varicella zoster virus or cytomegalovirus. HIV was isolated from only 14% of the 127 CSF specimens, but from 82% of CSF-paired blood samples. HIV antigen was detected in 12% of CSF specimens and 44% of paired plasma samples. Twenty specimens analysed using the polymerase chain reaction (PCR) detected proviral DNA in 75% of CSF specimens. The low rate of virus recovery from CSF was caused by neither the freezing of specimens prior to culture nor therapy. In contrast, virus isolation from CSF was significantly associated with CSF cell count. Virus isolation and antigen detection in CSF were not correlated with either the Centers for Disease Control disease stage or the peripheral CD4+ lymphocyte count, whereas viraemia was significantly associated with a low CD4+ lymphocyte count. Moreover, virus isolation and antigen detection in CSF were not associated with symptoms of subacute HIV encephalitis, suggesting that these markers are not of potential value in the diagnosis of HIV-specific neurologic complications. The value of PCR in this field merits further investigation.