AIM: To study the effect of trapidil (Tra) on endothelin-1-induced proliferation of cultured rat aortic vascular smooth muscle cells (VSMC). METHODS: The [H-3]TdR incorporation into DNA assay, the number of VSMC, and cell cycle distribution were measured. RESULTS: Pretreated with endothelin-1 100 nmol.L-1, cell number, [H-3]TdR uptake, and cell mitogenic activity increased 134 % +/- 23 %, 210 % +/- 70 %, and 86 % +/- 18 %, respectively. This proliferation was inhibited by Tra 5, 50, 500 mu mol.L-1. The inhibitory rates were 12 % - 48 %, 35 % - 54 % and 15 % - 47 %, respectively. Tra did not influence the proliferation of VSMC without endothelin-l pretreatment. CONCLUSION: Tra antagonized the proliferation of VSMC induced by endothelin-1.