Sera from 31 patients with progressive systemic sclerosis (PSS), 5 patients with widespread localized scleroderma (LS), and 3 patients with lichen sclerosus et atrophicus were analyzed for aminoterminal propeptide of type III procollagen (PIIINP) using a radioimmunoassay based on human propeptide. Thirty-eight per cent of the patients with PSS had levels above normal range, including all of the 3 patients with diffuse scleroderma. The same applies to 4 of 5 patients with widespread localized LS, while PIIINP in all 3 patients with lichen sclerosus et atrophicus were within normal levels. In patients with acrosclerosis, elevated PIIINP seems to be correlated to rapid progression and extension of lesions. A significant increase in PIIINP was found in a patient following discontinuation of prednisone and cyclophosphamide, while the present investigation did not allow judgement of effects of treatment with either penicillamine or cyclosporin A.