Small minipigs (Microminipig, registered as a novel variety of pig in Japan) were developed for use in non-clinical pharmacological/toxicological studies for new drug development. To assess the pharmacokinetics of selective substrates of human cytochrome P450s in Microminipigs, caffeine (human P450 1A2), warfarin (P450 2C9), omeprazole (P450 2C19), metoprolol (P450 2D6), and midazolam (P450 3A) were administered in combination, intravenously (0.20 mg kg(-1))( )or orally (1.0 mg kg(-1)). Plasma samples obtained, up to 24 hr after dosing, from four male and four female Microminipigs were analyzed by liquid chromatography tandem mass spectrometry to estimate typical pharmacokinetic parameters for each analyte. Bioavailabilities were approximately 80% for caffeine and warfarin, but less than 10% for omeprazole, metoprolol, and midazolam. No significant differences were noted, for the five probes, in area under the plasma concentration-time curve and peak plasma concentration values obtained from male and female Microminipigs. Clearance of caffeine, warfarin, omeprazole or midazolam in vivo, mediated mainly by cytochrome P450s 1A, 2C or 3A in Microminipigs, was similar to data reported for human. However, metoprolol metabolism, mediated by P450 2D enzymes in Microminipigs, was faster than reported for in vivo human kinetic parameters and in vitro in a human liver microsomal system. The results of this study suggest that the Microminipig is a suitable animal model for use in biological experiments for comparisons of pharmacokinetics of drugs in humans. The five-probes in combination used in this study demonstrate the disposition of typical P450 drugs in Microminipigs in vivo, with the aim of use in non-clinical pharmacological/toxicological studies.