Myofibroblasts play an important role in normal wound healing. They are present transiently during tissue repair. Their differentiation from fibroblasts and their role in granulation tissues are most likely to be modulated by cytokines. As these cells are derived from normal fibroblasts, their responses to cytokines are assumed to be similar. Until now, however, the difficulties in obtaining and maintaining normal human wound healing myofibroblastsin vitrohave hampered comparison. The present study was designed to determine the effect of TGF-β1 and IFN-γ, two cytokines known to modulate fibroblast morphology, on wound healing myofibroblasts and to compare it to fibroblasts. Morphological and phenotypic changes were followed by light and electron microscopy (stress fibers) and immunofluorescence cytochemistry (α-SM actin). Functional parameters such as the capacity to synthesize collagen and collagen gel contraction were studied. Both cytokines induced a strong modification of growth rate and phenotypic and morphological parameters in fibroblasts whereas collagen synthesis was slightly changed. Furthermore, TGF-β1 increased contractile capacity of fibroblasts whereas IFN-γ greatly decreased it. In myofibroblasts, TGF-β1 and IFN-γ did not induce any variation of morphology or growth rate. Interestingly, a strong modulation of functional parameters was observed: collagen synthesis was highly modified and, as for fibroblasts, the contractile capacity was altered. However, inhibition of contraction by IFN-γ was irreversible in myofibroblasts but not in fibroblasts. These results suggest that fibroblastic cells show modulated responses to cytokines according to their stage of differentiation during wound healing.