Human recombinant-gamma-interferon was tested on human dental pulp fibroblast activity in vitro. Fibroblast proliferation was estimated by a colorimetric test. Type I and type III collagens and fibronectin were quantified by radioimmunoassay in culture supernatant from confluent fibroblasts. A dose dependent stimulation of the proliferation was observed when fibroblasts were treated with recombinant-gamma-interferon. In contrast, an inhibition of the synthesis of soluble types I and III collagen and fibronectin by confluent cell cultures treated with recombinant-gamma-interferon occurred without apparent modification of the insoluble collagen level in the cell layer. Quantimetric analysis of type I collagen immunoperoxidase labelling have demonstrated that there was no intracellular storage of type I collagen in these cultured fibroblasts. These data support the view that human recombinant-gamma-interferon can affect human dental pulp fibroblast functions and thus may play an important part in the regulation of fibrosis.