Skatole (3-methylindole, 3MI) is a microbial metabolite produced from tryptophan in the gastrointestinal tract of some species. In pigs, 3MI causes "boar taint", a fecal-like odour liberated when the pork is cooked. Only 5-10% of uncastrated male pigs accumulate 3MI at levels detectable by consumers. The reason for this is unknown. The hypothesis of the present research is that individual differences in 3MI metabolism determine 3MI accumulation in fat. A series of studies was conducted to determine the 'in vitro ' metabolism of 3MI by porcine liver microsomes and cytosol and to try to establish a relationship between 3MI enzymatic metabolism and 3MI accumulation in fat. Seven major metabolites were produced by hepatic microsomes during Phase I metabolism of 3MI. Three of these metabolites had already been identified and corresponded to 3-OH-3-methyloxindole (HMOI), 5-hydroxy-3-methylindole (5-OH-3MI) and 6-hydroxy-3-methylindole (6-OH-3MI). Four new metabolites were identified as 3-hydroxy-3-methylindolenine (HMI), 3-methyloxindole (3MOI), indole-3-carbinol (I3C), and 2-aminoacetophenone. The role of different cytochrome P450 enzymes in the production of these Phase I metabolites was investigated using different chemical inhibitors. Production of 3MI metabolites was affected by inhibitors of CYP2A6 and CYP2E1 and the CYP2A6 content/activity was negatively correlated (P < 0.05) with 3MI fat levels. In another study, the metabolism of HMI was investigated using porcine cytosol. It was determined that HMI is converted to HMOI by the enzyme aldehyde oxidase (AO) and that AO activity is negatively correlated (P < 0.05) with 3MI fat levels. Studies conducted to investigate the Phase II metabolism of 3MI showed that 5-OH-3MI is sulfated and glucuronidated and that a 3MI-glutathione conjugate is formed when microsomes are incubated with 3MI, NADPH and glutathione. The sulfotransferase involved in the sulfation of 5-OH-3MI was identified as the thermostable form of phenol sulfotransferase (TS-PST) and pigs with high levels of 3MI in fat consistently had very low TS-PST activity. The present research indicates that CYP2A6, AO and TS-PST play an important role in the metabolism of 3MI. The activity and/or levels of these enzymes could be used as marker for 3MI-induced boar taint. More research is needed to determine the regulation of these enzymes in the male adult pig.