The seed extract of Schisandra chinensis was investigated in the rat for its restorative or therapeutic effect on Phase I hepatic drug metabolism following intoxication by carbon tetrachloride (CCl4). Male Sprague Dawley rats (220-250 g) were divided into two sets, one included rats with or without CCl4 intoxication, the other included CCl4 intoxicated rats with or without treatment of Schisandra extract. With the treatment regimen, rats received four oral doses of Schisandra (160 mg/kg) or the same volume of water at 8, 24, 32 and 48 h after CCl4 intoxication. A single oral dose (80 mg/kg) of antipyrine, a conventional probe for oxidative drug metabolism, was then administered. The levels of liver serum transaminases and cytochrome P450 were measured and the pharmacokinetics of antipyrine were assessed using a non-compartmental approach via WinNonlin. In comparison to the rats without CCl4 intoxication (t1/2: 2.2 +/- 0.9 h; Cl/F: 0.30 +/- 0.01 L/h/Kg; P450: 0.611 +/- 0.190 nmol/mg protein), CCl4 administration significantly decreased elimination (t1/2: 12.0 +/- 3.9 h) and oral clearance (Cl/F: 0.049 +/- 0.018 L/h/kg) of antipyrine, and markedly reduced the content of P450 (0.075 +/- 0.011 nmol/mg protein). Data obtained from intoxicated animals treated by Schisandra extract, compared to those without treatment, showed significant (p < 0.05) improvement in the t1/2 (4.45 +/- 1.7 h) and Cl/F (0.096 +/- 0.018 ml/h) estimates of antipyrine and a 2-3 fold increase in P450 level (0.190 +/- 0.072 nmol/mg protein). Findings in this study suggest that the seed extract of Schisandra appeared to be a promising agent for the improvement of Phase I oxidative metabolism in the liver damaged by CCl4.