Previous studies have indicated that fetal skin fibroblasts display an elevated level of migratory activity compared to adult cells and that this may result from inherent differences in the production of hyaluronan (HA) by these cells. Data presented in this communication indicate that the elevated level of fetal fibroblast migration into 3D-collagen gels and HA synthesis by these cells were not affected by epidermal growth factor (EGF), platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) or basic fibroblast growth factor (bFGF). In contrast, both cell migration and HA synthesis by fetal fibroblasts were inhibited by transforming growth factor-beta1 (TGF-β1). Adult fibroblasts responded to these cytokines in a distinct fashion: i.e. cell migration and HA synthesis were stimulated by EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-β1. Gel-filtration chromatography revealed that these effects of cytokines on HA synthesis were predominantly confined to the production of high molecular mass (>10⁶ kDa) species. Co-exposure of cells to both cytokines and Streptomyces hyaluronidase revealed that (1) the elevated migration of control fetal fibroblasts was inhibited by hyaluronidase, (2) this inhibition was partially restored by co-exposure to EGF, PDGF, aFGF and bFGF, but remained unaffected by TGF-β1, (3) the migration of control adult fibroblasts was unaffected by hyaluronidase and partially stimulated by EGF, aFGF and bFGF (when compared to the effects of these cytokines on cells cultured in the absence of hyaluronidase) and (4) neither PDGF nor TGF-β1 affected the migration of hyaluronidase-treated adult cells. Linear regression analysis revealed a significant correlation between cell migration and HA synthesis by both fetal and adult fibroblasts in the presence and absence of cytokines (r²=0.9277, P<0.0001), with the exception of adult fibroblasts exposed to PDGF. Taken together, these findings suggest that (1) the migration of fetal and adult fibroblasts is differentially modulated by exogenous cytokines and (2) with the possible exception of the effects of PDGF on adult fibroblasts, cytokine-induced modulation of cell migration appears to utilise both HA-dependent and HA-independent pathways.