Copper is implicated in the pathogenesis of several fibrotic disorders. Areca nut has been shown to have a high copper content and areca chewing is associated with oral submucous fibrosis (OSF). The effects of copper on human oral fibroblasts were investigated in vitro. Human oral fibroblasts were incubated with copper chloride (CuCl2) at concentrations ranging from 0.01 microM to 500 microM for 24 h, and in vitro cell proliferation was assayed by incorporation of tritiated-thymidine; soluble and non-soluble collagen synthesis was assayed using tritiated-proline. Addition of copper chloride at concentrations ranging from 0.1 microM to 50 microM increased the collagen synthesis by the oral fibroblasts compared with growth without copper (P