The purpose of this study was to determine whether exposure of chemically transformed golden Syrian hamster oral epidermoid carcinoma cell (HCPC-1) cultures to smokeless tobacco extract (STE) is associated with a decrease in specific angiotensin I-converting enzyme (ACE) activity and whether this decrease potentiates bradykinin-induced cell growth. We found that STE induced a significant concentration- and time-dependent decrease in ACE activity in cultured HCPC-1 cells (P <0.05). STE alone had no significant effect on cell number. Bradykinin alone induced a slight, but significant, increase in cell number (P <0.05). These effects were signific potentiated by STE (P <0.01). We conclude that STE potentiates bradykinin-induced HCPC-1 cell growth, in part by attenuating specific ACE activity in these cells.