Scl 70 antibodies were tested for in 107 patients with systemic sclerosis: 68 with acrosclerosis and 39 with diffuse scleroderma. Anticentromere antibodies (ACA) and other antinuclear antibodies (ANA) were tested for by indirect immunofluorescence on HEp-2 cells. Positive results for Scl 70 antibodies were obtained in 77% of cases of diffuse scleroderma and 44% of acrosclerosis. ACA and Scl 70 antibodies were found to be mutually exclusive. If acrosclerosis cases positive for anticentromere antibodies are excluded, the percentage of acrosclerosis cases positive for Scl 70 was 63%. ACA were found to be a marker of a benign, abortive subset of acrosclerosis with almost no cutaneous involvement (CREST), whereas Scl 70 did not discriminate between acrosclerosis and diffuse scleroderma. On HEp-2 cells Scl 70 positive sera gave a characteristic, fine speckled, almost homogeneous nuclear staining pattern.