['The contribution of the polymorphism of complement C4A and C4B alleles to the pathogenesis of systemic sclerosis (SSc) was studied in Japanese patients.', 'C4A and C4B typing was carried out in 44 SSc patients and in 83 normal subjects using electrophoresis followed by immunofixation and immunoblotting. HLA-DR typing and HLA DRB1*15 and *08 genotyping were carried out by the PCR method and the PCR-SSCP method, respectively.', 'In SSc with diffuse scleroderma, the frequency of C4BQ0 was significantly increased (44.4%, p < 0.001, pc < 0.01). In SSc with antitopoisomerase I antibody (a-Scl-70) C4BQ0 was also increased (50.0%, p < 0.001, pc < 0.01). Association analysis indicated that the increase in C4BQ0 was not primary but reflected an increase in HLA-DRB1*1502. In contrast, C4A/Q0 was significantly increased in limited scleroderma (53.8%, p < 0.005, pc < 0.05) and SSc without a-SCL-70 (53.8%, p < 0.005, pc < 0.05).'] Are c4A and C4B null alleles genetic markers of different types of systemic sclerosis in Japanese patients?