Abstract: AimTo investigate the effects of NPPB, a chloride channel blocker, on proliferation of mesangial cells. MethodsCell proliferation was determined by measuring cell number and ³H-thymidine incorporation. The LDH activity released from these cells was measured as evaluation of cell viability. The phase of cell cycle was detected by flow cytometry. ResultsCell proliferation assays showed that treatment with both NPPB (50 and 25 μmol·L^-1) and in hypertonic media (100% increased osmolarity with D-mannitol ) significantly reduced the number of human MC and ³H-thymidine incorporation in a dose-dependent manner. But the LDH activity was not significantly altered in the treatment with 50 μmol·L^-1 NPPB. Flow cytometry experiments showed that 50 and 25 μmol·L^-1 NPPB arrested (84.2±2.4)% and (80.8±2.9)% of cells at G0/G₁ stage, versus (70.5±1.4)% of control cells. Conclusion NPPB suppresses cell proliferation and produces growth arrest at G0/G₁ phase in human MC by a mechanism probably associated with changes in cell volume.