The HLA-A, -B, -C and -D were determined in 200 multiple sclerosis (MS) patients, 64 of whom underwent a CSF examination. Their frequencies were correlated with the rate of disease progression and with factors thought to influence disease progression, including onset age, type of clinical course and intrathecal IgG synthesis. No correlation was found between HLA haplotypes and progression rate or type of disease course. Patients starting MS after age 31 years carried the DR2 determinant more frequently (P = 0.016) than patients with onset before this median age. Although the greatest proportion of patients with an IgG index greater than 1.5 or more than 15 oligoclonal bands in their CSF were DR2 carriers, no statistical difference was found in the intrathecal IgG synthesis of HLA-DR2 (+) and (-) patients.