PURPOSE: Insulin-like growth factor-1 (IGF-1) promotes the proliferation and migration of penile cavernous smooth muscle cells in the rat. The goals of this study were to evaluate the expression of IGF-1 and IGF-1 receptor (IGF-1R) in human corpus cavernosal smooth muscle cells (HCCSMCs) and to investigate the effect of IGF-1 on the proliferation of these cells in vitro. MATERIALS AND METHODS: The HCCSMCs were cultured from five impotent patients. The smooth muscle cells were identified by immunofluorescent stain. Total RNA was extracted, and IGF-1 gene expression was determined by RT-PCR. The IGF-1R immunoreactivity was examined by fluorescent Immunocytochemistry. Cell growth was assessed with a novel proliferation assay based on bioreduction of the fluorescent dye, Alamar blue. RESULTS: Endogenous IGF-1 mRNA expression was detected by RT-PCR analysis. The HCCSMCs were positive for IGF-IR. The proliferation of HCCSMCs increased with the dose in response IGF-1 in the culture medium in concentrations up to 100 ng/ml. CONCLUSIONS: Both IGF-1 and IGF-1R are expressed endogenously in human corpus cavernosal smooth muscle cells. IGF-1 promotes the proliferation of these cells in vitro.