Anticentromere antibodies (ACA) and anti–topoisomerase I (anti–topo I) were assayed in serum samples from 355 patients: 89 with proximal scleroderma; 54 with CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias), without proximal scleroderma; 154 with primary and secondary Raynaud's disease; and 58 with other rheumatic diseases, without Raynaud's disease. Sera from healthy control subjects were also assayed. Using immunoblotting techniques, anti-topo I was detected in 28% of the patients with proximal scleroderma; using immunodiffusion techniques, this antibody was found in only 20% of the same group of patients. Anti–topo I and ACA were found primarily in patients with scleroderma, CREST syndrome, and Raynaud's phenomenon. ACA identified patients with less severe disease, whereas anti–topo I identified patients with skin and cardiac involvement and patients with malignancies.