The biotransformation of S-warfarin was examined using liver microsomes prepared from rats 6-96 hr after treatment with a necrotizing dose (5.6 mmoles/kg) of thioacetamide. Four catalytically distinct classes of enzyme activity were observed which declined in activity with different half-lives after thioacetamide intoxication. S-Warfarin 7-hydroxylase activity was destroyed with a half-life of 16.6 +/- 3.1 hr. 6-Hydroxylase activity was destroyed with a half-life of 25.3 +/- 3.0 hr. 4'-Hydroxylase activity was destroyed with a half-life of 34.6 +/- 4.8 hr, which paralleled the loss of total hepatic cytochrome P-450 with a half-life of 33.4 +/- 3.6 hr. Production of an unidentified metabolite was not affected by thioacetamide intoxication during the first 48 hr. The ratio of rates of product formation were used as an alternative method to test the homogeneity of distinct enzyme catalytic activities. The ratio of measured responses (e.g. chromatographic peak heights) was used directly to determine the product ratios, provided that the rate of formation of each product was directly proportional to the experimentally measured response for each product. The use of product response ratios to discriminate between catalytic activities was inherently more precise because calibration errors were eliminated. Differences in the rates of destruction of warfarin hydroxylases provided further evidence of the multiplicity of hepatic mixed-function oxidases and suggested topographical differences in their location within the liver lobule.