Upon evaluation of 40 subjects with progressive systemic sclerosis (PSS), a significant association of HLA antigens A9 and Aw24 (a subgroup of A9) was found with diffuse scleroderma. HLA-Aw23 (a second subgroup of A9) was also increased in the patients, however, this was not statistically significant. Diffuse scleroderma appears to be one of the few diseases that shows an association with the HLA-A locus.