Unconcentrated cerebrospinal fluid (CSF) samples from 50 patients with subacute sclerosing panencephalitis (SSPE) were investigated by rocket immunoelectrophoresis (RIE) against anti-human IgG sera. Two patterns of immune precipitates were observed: precipitates with exclusively cathodal and precipitates with bipolar extension. Hemagglutination-inhibition tests against measles virus antigen were performed after absorption of the CSF samples with Protein A-containing Staphylococcus aureus and treatment with 2-mercaptoethanol. The results point to different pathological significances of the precipitation line anomalies revealed by RIE, that might be relevant for some of the patients investigated.