The clinical and renal histologic attributes of 135 systemic lupus erythematosus (SLE) patients with DNA and/or Sm antibodies were compared to determine if the presence of the Sm antibodies served as a marker for a specific subset of SLE. Although Raynaud's phenomenon was more frequent in patients with Sm antibodies (P less than 0.005), serious central nervous system disease was over three times as common in patients with DNA antibodies (P less than 0.005). Only one of 23 patients with Sm antibodies had diffuse proliferative glomerulonephritis on renal biopsy, whereas 6 of 14 patients with only DNA antibodies had this histologic finding (P = 0.01). The Sm antibody system may therefore identify a subset of SLE patients with milder central nervous system and renal disease.