Full thickness biopsies of affected skin and fascia from one patient with diffuse fasciitis and eosinophilia (DF), two patients with generalized morphea (GM), and five patients with progressive systemic sclerosis (PSS) of recent onset were examined for the expression of transforming growth factor beta 1 (TGF beta 1) and type I procollagen genes by in situ hybridization with human sequence-specific cDNA. An increased number of fibroblasts showing clearly detectable expression of pro alpha 1(I)collagen gene was found in all fibrotic lesions when compared with unaffected skin from the patient with DF and skin from two normal individuals examined in parallel. Expression of the TGF beta 1 gene was noted in a fibroblast subpopulation of the affected tissues from the patients with DF and GM. In contrast, the TGF beta 1 gene was not expressed at a detectable level in affected skin from the five patients with PSS. The results suggest that TGF beta 1 may play a role in the development of skin fibrosis in cases of DF and GM. However, from these studies, we cannot implicate TGF beta 1 in the pathogenesis of skin fibrosis in PSS.