Nodular palmar fibromatosis is a self-limited proliferation of fibro-/myofibroblasts associated with growth factor synthesis and abundant fibronectin extracellular matrix deposition. bFGF and TGF beta are potent modulators of fibro-/myofibroblast proliferation and differentiation. Moreover, in vitro investigations evidenced a TGF beta 1-dependent regulation of alternative splicing of fibronectin mRNA. To investigate a possible implication of these growth factors in the tissue formation process of palmar fibromatosis, TGF beta 1/2 and bFGF synthesis, as well as TGF beta 1/3 and bFGF tissue distribution, is demonstrated by RNA in situ hybridization and/or immunohistochemistry in relation to myofibroblast phenotype development (alpha-smooth muscle actin, desmin immunohistochemistry), expression of different fibronectin isoforms (ED-A+, ED-B+ and oncofetal glycosylated fibronectin immunohistochemistry, fibronectin RNA in situ hybridization) and cellular activity (cyclin RNA in situ hybridization, Ki-67 immunolabelling). The myofibroblast phenotype (alpha-smooth muscle actin, desmin), the growth factor synthesis (TGF beta 1 and 2, bFGF), fibronectin matrix synthesis (RNA in situ hybridization with cDNA) and ED-A+, ED-B+ and oncofetal glycosylated fibronectin immunostaining are exclusively localized in the active proliferative nodules (Ki-67 immunolabelling and cyclin mRNA demonstration). Whereas the growth factor synthesis is restricted to the proliferative areas of the fibromatosis only, TGF beta 1, TGF beta 3 and bFGF proteins can also be detected immunohistochemically with a lower intensity in the surrounding aponeurotic tissue. The spatial correlation of myofibroblast phenotype, TGF beta and bFGF synthesis and the occurrence of the oncofetal molecular fibronectin variants (ED-B+ and oncofetal glycosylated fibronectin) in the active proliferative fibromatosis nodules suggests a pathogentic role of these growth factors and matrix components in the tumorous tissue formation process. The presence of the bFGF and TGF beta 1/3 proteins in fibroblasts neighbouring the proliferative nodules may point to a recruitment of quiescent aponeurotic fibroblasts in the fibromatous tissue formation process.