Serum samples collected from 69 patients with multiple sclerosis (MS) living in the Hautes-Pyrénées county were tested for immunoglobulin Gm gamma 1, gamma 2, and gamma 3, heavy chain allotypes (Gm system), and immunoglobulin light chain Kappa (Km system). A control group was made up of normal individuals living in the same county. We found a significant excess of individuals with Gm3; +/- 23;5/Gm3; +/- 23;5 amongst the MS patients as compared with controls (relative risk = 2.4). A slight increase of the Km (1) frequency was found in MS patients compared with controls, 21.7% vs 11.8%, but this difference was not significant.