The elimination of caffeine from plasma and the excretion of the main metabolites of metamizol (noramidopyrinemethanesulphonate sodium) into the urine were determined in healthy pregnant women (weeks 30-38 of pregnancy) and in patients with intrahepatic cholestasis in pregnancy (weeks 28-39 of pregnancy). From the elimination velocity of these model substances conclusions concerning the activity of 3-methylcholanthrene (caffeine elimination) and phenobarbital inducible isoenzymes (metamizol elimination) of cytochrome P-450 are drawn. Patients with intrahepatic cholestasis in pregnancy (t1/2 = 15.8 +/- 1.8 h) eliminate caffeine more slowly than healthy pregnant women (t1/2 = 11.0 +/- 0.8 h) at this stage of pregnancy. The excretion of the metabolites of metamizol is only in tendency diminished in patients with intrahepatic cholestasis. The influence of the intrahepatic cholestasis on the cytochrome P-450 isoenzymes investigated differs in degree.