The capacity of liver microsomes to oxidize various substrates known to be specific of alcohol-inducible cytochrome P-450 was studied in rats treated with different xenobiotics such as 3-methylcholanthrene, phenobarbital, acetone, and ethanol. Analysis of results showed a significantly marked increase following ethanol and acetone treatments of the p-nitrophenol hydroxylation (283 +/- 19% and 304 +/- 21%), N-nitrosodimethylamine (NDMA) demethylation (280 +/- 105% and 228 +/- 95%), benzene hydroxylation (258 +/- 60% and 236 +/- 61%), butanol oxidation (173 +/- 34% and 154 +/- 32%), aniline hydroxylation (147 +/- 22% and 95 +/- 8%), and ether de-ethylation (95 +/- 17% and 83 +/- 17%) and a not significant increase of N-nitrosodiethylamine (NDEA) de-ethylation (34 +/- 11% and 9 +/- 8%) in rat microsomes, respectively, versus control animals (mean +/- SD, values expressed as nmol/min/nmole P-450). All of these activities significantly decreased after 3-MC treatment, except for the p-nitrophenol hydroxylation. PB treatment markedly enhanced NDEA de-ethylation, p-nitrophenol, and benzene hydroxylations (106 +/- 38%, 109 +/- 14%, and 153 +/- 62%, respectively) versus controls. These results suggest that NDMA and especially 1-butanol are the most specific and useful probes of alcohol-inducible cytochrome P-450 in crude liver microsomes.