CSF and matched serum antibody titres to seven common viruses were measured in 20 chronic schizophrenic patients, and 17 of these were age and sex-matched with orthopaedic controls. CT scans were carried out in patients and age and sex-matched radiological controls. There was a trend for CSF viral antibody titres (except CMV, HSV and VZV) to be decreased in the patients compared to controls, statistically significant for mumps and IgG. The CSF/serum ratios showed a reduction in the patients, compared to controls, statistically significant for measles and rubella as well as mumps and IgG. Cerebral ventricular size was significantly increased in the patients compared to controls, but did not correlate with any of the antibody data. These findings suggest that there is a reduced immune response to certain common viruses in the CNS of schizophrenic patients, but possible effects of institutionalisation or current medication could only be adequately excluded by further prospective studies.