Detection of cytomegalovirus (CMV) DNA by the polymerase chain reaction (PCR) in samples of cerebrospinal fluid (CSF) has been shown to be a sensitive method of diagnosing CMV disease in the central nervous system. Since CMV causes latent infection in white blood cells, an unanswered question is whether detection of latent CMV DNA in the cell fraction of CSF samples by PCR is possible in seropositive patients. In a prospective study, the finding of CMV DNA in CSF of CMV seropositive patients with suspected viral infection of the central nervous system (CNS) was evaluated clinically. Fractionation of 64 CSF samples from seropositive patients was carried out before analysing the samples for CMV DNA by PCR. In four of the five patients who had CMV DNA in the cell pellet and/or supernatant, the clinical data suggested CMV-associated neurological disease. The remaining 59 samples were negative in both pellet and supernatant. In addition, 11 CSF samples with high cell counts from patients with bacterial meningitis were examined for CMV DNA and found to be negative in 10 patients and positive in 1. One hundred thirty two uncentrifuged CSF samples were used as negative controls. The results of the study indicate that detection of CMV DNA in CSF samples by PCR correlated well with disease and was not due to latent CMV infection.