This study examined the role of heme oxygenase (HO) in the acquisition of resistance to hydrogen peroxide (H2O2) and hemin toxicity by renal epithelial cells (BSC-1). BSC-1 cells adapted by long-term exposure to H2O2 exhibited a twofold increase in basal HO activity and expression of HO-1 mRNA as compared with their wild-type counterparts. Exposure of both adapted and wild-type BSC-1 cells to H2O2 induced HO-1 mRNA. When cells were exposed to H202 for 24 hours, cell viability was reduced; however, an inhibitor of HO activity, Zn 2,4-bis-glycol protoporphyrin IX, improved cell viability. In a similar manner, ZnDBG completely overcame the reduction in cell viability brought about by 1 hour of hemin treatment. In addition, cells preexposed to hemin for 24 hours maintained a high level of HO mRNA and acquired resistance to further challenge with H2O2. Hemin treatment per se was associated with a detectable reduction in BSC-1 cell viability; however, the effect of hemin was not additive to the cytotoxicity of hydrogen peroxide, suggesting a common pathway of cell injury. In conclusion, two interrelated stressors, H2O2 and hemin, produced a stimulation of HO-1, and this was associated with a reduction in the viability of BSC-1 cells. Long-term exposure (24 hours) to both stressors resulted in the acquisition of some resistance to a further acute challenge of oxidant stress in BSC-1 cells.