Sera from 33 patients with scleroderma were examined for immunofluorescent reactivity with viable or acetone-fixed fibroblasts. All 33 sera reacted with the cell surface membranes of viable fibroblasts. 23 of 33 sera (70%) also reacted with nuclei of acetone-fixed fibroblasts. The commonest nuclear staining pattern was homogeneous (46%) followed by nucleolar (36%) and speckled (23%). 70% showed more than 1 staining pattern in the same serum. Antibody titres of homogeneous and nucleolar staining patterns (1:8 to 1:1024) were generally higher than those of the speckled pattern (1:8 to 1:256). No change in pattern or titre was noted in sera from 4 patients over a 10-12 month period. Antibody in sera with homogeneous or nucleolar staining patterns belonged to one or more of the 3 major antibody classes, IgG, IgM or IgA while antibody in sera with a speckled nuclear pattern belonged to the IgM class only. No correlation was found between the pattern of anti-nuclear reactivity and visceral involvement.