The relationships between the level of skatole in backfat, the rate of skatole metabolism in isolated liver microsomes, hepatic cytochrome P450IIE1 content and mRNA levels were investigated in Large White ✕ Landrace (LW) and the Meishan ✕ Landrace (M) breeds. A method based on thin layer chromatography was developed and used for measurement of microsomal skatole metabolism. Skatole metabolism by liver microsomes was inhibited by diallyl sulphide, a specific inhibitor of cytochrome P450IIE1 but not by inhibitors of other P450 isoforms. We have shown that the rate of skatole metabolism by liver microsomes was proportional to the microsomal P450IIE1 content. In LW pigs there was considerable variation in cytochrome P450IIE1 expression and P450IIE1 protein level and there was a significant negative correlation between backfat skatole level and hepatic microsomal cytochrome P450IIE1 content. Pigs exhibiting low P450IIE1 content in general also showed low levels of P450IIE1 mRNA. These results show that the levels of deposition of backfat skatole in LW pigs are inversely related to the rate at which skatole can be metabolized by liver microsomes, and this in turn depends on the level of expression of cytochrome P450IIE1 mRNA in the liver. In the M breed generally the P450IIE1 protein and mRNA levels were very low and backfat skatole level was high. However the skatole level varied over a 10-fold range and there was no significant correlation with P450IIE1 protein or mRNA content. The M breed was shown to express high levels of the multidrug resistance protein in liver, and it is suggested that export of skatole from liver via this transport protein may be an additional factor regulating backfat skatole in M pigs, but not in the LW breed.