To investigate the effects of pyrrolidine dithiocarbamate (PDTC) on the proliferation and PCNA (proliferating cell nuclear antigen) expression of cultured human retinal pigment epithelium cells, human retinal pigment epithelium cells (RPE) were cultured from normal adults who died accidentally. The effects of PDTC on the proliferation of RPE cells were examined by using methyl thiazlyl tetrazolium (MTT) assay. The effects of PDTC on the PCNA expression of RPE cells were immunohistochemically examined by employing biological image analysis system (BIAS). After treatment with PDTC of various of concentration ranging from 0.062 to 1 g/L for 24 h, or concentrations ranging from 0. 031 to 1 g/L, the proliferation of RPE cells decreased in a dose-dependent manner. After treatment with PDTC of concentration varying from 0. 062 to 1 g/L for 24 h, the PCNA expression was also suppressed in a dose-dependent manner. It is concluded that PDTC can inhibit the proliferation of RPE cells in vitro in a dose-and time-dependent manner, at least in part,by down-regulating the expression of PCNA. PDTC may be used to prevent and treat the proliferative vitreoretinopathy (PVR).