In serum-free media, tertatolol does not significantly alter the incorporation of ³ H-thymidine after 28 h of incubation in human mesangial cell (HMC). In the presence of 1% serum, tertatolol significantly reduces ³ H-thymidine incorporation. Tertatolol also inhibits ³ H incorporation when PDGF and thrombin are used as the stimulus. Tertatolol inhibits the reduction in planar surface area of HMC induced by angiotensin II. The inhibitory effect of tertatolol on HMC proliferation is also potentiated by ritanserin and MDL 72222, 5HT2 and 5HT3 antagonists, respectively.