• Sera from two multiparous wives of patients with multiple sclerosis (MS) were used to detect B cell antigens in other patients. With serum X, 11 of 16 patients were positive as compared with ten of 16 controls (.05 < P <.1). With serum Y, a positive response was found in 11 of 16 patients and two of 23 controls (P <.0005). Ten of the 11 patients who were positive with serum Y were also HLA-Dw2, which suggests that the B cell antigen detected by this serum is linked to Dw2. Three of four Dw2-positive controls were negative with serum Y, which raises two alternative hypothetical possibilities concerning the B cell antigen. These findings indicate that serum from multiparous wives may be an important tool in the investigation of the genetic components associated with MS.