Fourteen Finnish families, each with two or more cases of multiple sclerosis (MS), were analysed for HLA antigens. Seventy family members were studied. They were all born in a high-risk area of MS and came from families with an unusually high frequency of MS. The frequencies of B7, B12 and DR2 were increased both in patients and their healthy relatives, whereas A1, B8 and DR1 were decreased in patients. MS patients shared the HLA haplotypes more often than expected.