Twenty histocompatibility antigens of the 1st and the 2nd HL-A series have been determined in 200 MS patients and 255 randomly-selected healthy individuals of West Germany. Both groups differed significantly in 2 antigens of the 1st, and 2 of the 2nd HL-A series. Whereas the antigens HL-A3,HL-A10 and W5 were found more frequently in multiple sclerosis (MS) patients than in controls, the opposite was true for the antigen HL-A12. Brief comments as to the possible biological meaning of these findings are given.