An investigation of class II histocompatibility antigens was carried out in patients with definite diagnosis of multiple sclerosis (MS) according to Poser's criteria. There were 42 patients from Warsaw and 98 patients from Gdańsk. Histocompatibility antigens were assayed with microlymphocytotoxicity test. 6 antigens on locus DR and 1 antigen on locus DQ were evaluated. The antigen frequencies were compared in the two groups using the chi-square test. The antigen HLA-DQw1 occurred significantly more frequently in MS patients compared to healthy control group. Antigens HLA-DR2 and DR3 occurred more frequently in patients from Gdańsk than Warsaw region.