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More than 300 sera from patients with a connective tissuedisease were analyzed with the immunoblotting technique. Thepresence of autoantibodies against an 86,000-mol wt markerantigen for diffuse scleroderma (Scl-86) was found in 14 outof 33 patients with scleroderma. The presence of anti-Scl-86antibodies seemed to correlate with the diagnosis of diffusescleroderma since they were found in 13 out of 22 diffusescleroderma patients and in only one out of 11 patients withlimited scleroderma. All scleroderma sera (33 patients' seraand 13 reference sera) were also tested for the presence ofanti-Scl-70 antibodies. It was found that all anti-Scl-70 positivesera (n = 25) contained anti-Scl-86 antibody as well, suggestinga relationship between these two antigens. However, the Scl86antigen was shown to be an extremely insoluble nonchromosomalprotein, resistant to boiling in sodium dodecyl sulfate.This contrasts with the Scl-70 antigen, which has been describedas a thermolabile, soluble antigen present in the chromatinfraction. Together, our results are consistent with the idea thatScl-70 is a degradation product of Scl-86.The Scl-86 antigen is present in freshly prepared rabbitthymus, spleen, and liver nuclei as well as in nuclei fromvarious cultured cell lines, but is not detectable in extractablenuclear antigen from rabbit thymus.In a limited retrospective study, the anti-Scl-86 antibodieswere found in two sera from patients with Raynaud's phenomenonbefore the development of diffuse scleroderma. Therefore,it is possible that screening of patients' serum for this antibodymight predict the development of diffuse scleroderma.