There is evidence that an increase in cytosolic Ca++ concentration is a terminal event in the progression to cell death in toxic liver injury. We have compared the hepatoprotective effects ofN‐acetylcysteine (1 g/kg) and the calcium channel blocking agent, diltiazem (24 mg/kg), when given at 30 min, 3 h and 6 h after single intraperitoneal overdoses of acetaminophen (500 mg/kg) in mice. Overall beneficial effects on mortality, liver necrosis score, and plasma alanine aminotransferase (ALT) activity were found in diltiazem‐treated mice 24 h after acetaminophen overdose. However, the most marked effects were obtained when diltiazem was given 6 h after acetaminophen.N‐acetylcysteine was more effective than diltiazem at 30 min and 3 h, although it was less effective at 6 h. Mean plasma concentrations of the mercapturate metabolite (hepatic oxidative metabolism) were not significantly different among animals receiving acetaminophen alone or in combination with diltiazem, which suggests that the hepatoprotective effects of diltiazem are not exerted by inhibition of drug metabolic en