The apoptotic index (AI) of peripheral blood lymphocytes (PBL) and plasma corticosterone (CS) levels were determined in Wistar rats treated with phenytoin (PHT) at therapeutic and toxic doses (100 or 200 mg/kg/day, respectively, over a period of 7 days) and stressed by bifrontal electric shock (60 Hz/40 mA/0.2 seg). The values of CS and AI were found to be significantly higher in rats submitted to electric shock (ES) and in rats treated with therapeutic and toxic doses of PHT plus ES, than in rats treated only with PHT (P