Scleroderma (progressive systemic sclerosis; PSS) is a connective tissue disorder in which excessive collagen is deposited in the skin and internal organs. Mediators of abnormal fibroblast function in PSS have not yet been identified. Our objective was to examine the possibility that factors present in serum from patients with PSS, or in culture medium conditioned by PSS fibroblast growth, serve to regulate fibroblast function. Fibroblasts from affected and unaffected skin sites of patients with PSS and from normal adult skin were cultured in the presence of various human sera or conditioned media. Results indicate that (1) the proliferative influence of serum of patients with PSS is not different from that of normal donors, (2) increased proliferation and procollagen gene expression are not linked in affected or unaffected dermal fibroblasts, and (3) affected PSS fibroblasts produce a stimulatory factor(s) for procollagen gene expression to which they are differentially sensitive.