When HeLa cells were used as the substrate for detection by the indirect immunofluorescence method, antinuclear antibodies were demonstrated in 16 of 22 (72.7%) sera from patients with localized scleroderma. When mouse kidney sections were used, the positive rate for antinuclear antibodies was 50% (11 of 22). In the 3 subgroups of localized scleroderma, frequencies of antinuclear antibodies on HeLa cells were as follows: morphea, 50% (2 of 4), generalized morphea, 100% (6 of 6), linear scleroderma, 67% (8 of 12). Antibodies to centromere, Scl-70, nuclear RNP, Sm, and SS-B antigens were not detected in any patients with localized scleroderma. The high frequency of antinuclear antibodies in localized scleroderma sera suggests that localized scleroderma is a disease which, though different from diffuse scleroderma, also involves an immunologic abnormality.