Exposure of renal epithelial cells to PS-341 in concentrations < 22nM does not produce cytotoxicity. To determine the sensitivity of HK-2 cells to PS-341, cells were incubated overnight in medium containing PS-341 in concentrations between 0.8 and 200nM. Although concentrations up to 7mM were well tolerated, cell loss was observed at 22 and 200nM.