The frequencies of the HLA antigens A3, B7, and Dw2, previously related with multiple sclerosis, were investigated in 26 patients with acute aseptic meningitis and oligoclonal immunoglobulins in cerebrospinal fluid (CSF), but not in serum when investigated by agarose gel electrophoresis. HLA antigen frequencies were similar in patients with aseptic meningitis and controls. The oligoclonal immune response within the central nervous system in aseptic meningitis is not associated with the same HLA antigens found in patients with multiple sclerosis.