Aim To examine the role of Cl- channels in fetal calf serum (FCS) induced proliferation of vascular smooth muscle cells (VSMC). Methods Through cell count and 3 H-TdR incorporation, together with i measurement technology of fura-2 fluorescence, we studied the effects of Cl- channel blockers on proliferation of VSMC induced by FCS. Results Cl- channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS, 0.01 μmol/L～0.1 mmol/L) inhibited 5%FCS-induced increase in cell count and 3 H-TdR incorporation into VSMC, this inhibition was time and dose dependent. Other Cl- channel blockers such as indanyloxyacetic acid (IAA-94,0.1 μmol/L～1 mmol/L), 5-nitro-2-(3-phenylpropylamino)-benzonic acid (NPPB, 0.1 μmol/L～1 mmol/L),diphenylamine-2,2'-dicarboxylic acid (DPC, 0.1 μmol/L～1 mmol/L),4-acetamido-4'-isocyanatostilbene-2,2'-disulphonate (SITS,0.1 μmol/L～1 mmol/L) and furosemide (10 μmol/L～1mol/L), however, had no obvious effects (P>0.05, n=7 for cell count and n=8 for 3 H-TdR incorporation), and DIDS had no direct effect on voltage-gated calcium channel. Conclusion FCS can open DIDS-sensitive Cl- channel, and this channel may play an important role in modulating the proliferation of VSMC induced by FCS.