Serological studies were performed on sera from 66 patients with the clinical picture of systemic lupus erythematosus (SLE). These sera failed to give a positive antinuclear antibody test when tested on cryostat sections of mouse liver and thus these patients' sera appear to be ANA negative. Precipitating antibodies to the cytoplasmic antigen Ro were found in 41 cases and of the remaining 25 sera, 18 were found to have antibodies to single stranded DNA detectable by radioimmunoassay. Thus, 50 of the 66 patients exhibited serological findings which are commonly found in ANA positive SLE patients. Studies with KB cells as immunofluorescent substrate revealed that 66% of these sera were positive for nuclear staining demonstrating that at least part of the failure of these sera to stain mouse liver is due to antigenic deficiency of this substrate. The clinical picture of these patients was dominated by a severe photosensitive dermatitis but more than half of the patients had widespread multisystem disease. As a group these patients had a low frequency of nephritis and neuropsychiatric disease. Detection of these antibodies relates these patients serologically to other SLE patients and suggests that they are best perceived as part of the clinical spectrum of SLE.