The ratios of the scoparone O-demethylation products scopoletin to isoscopoletin were determined for reconstituted complexes of NADPH-P-450 reductase and each of four P-450 isozymes in a 2:1 molar ratio with a 1:1 mixture of [7-O-methyl-14C]- and [6-O-methyl-14C]-scoparone as substrate. The two phenobarbital inducible forms P-450PB-B and P-450PB-D have a 1:0.8 +/- 0.05 scopoletin to isoscopoletin ratio, and the two beta-naphthoflavone inducible forms P-450 beta NF-B and P-450 beta NF/ISF-G have ratios of 1:4.4 +/- 0.1 and 1:3.8 +/- 0.1, respectively. The scoparone-O-demethylation activities of the reconstituted preformed complexes of the four P-450 isozymes are given.