Six patients (4 women and 2 men, age between 60 and 90 years), subjected to right hemicolectomy, were gut donors. The mucosa was isolated from the last portion of the ileum and the first portion of the colon. Tissue specimens were free from pathological changes. The activities of the enzymes of phase I (NADPH cytochrome c reductase, ethoxycoumarin O-deethylase, aminopyrine N-demethylase, microsomal epoxide hydrolase, cytosolic epoxide hydrolase, glutathione reductase and glutathione peroxidase) and the enzymes of phase II (glutathionetransferase, glucuronyltransferase, acetyltransferase, thioltransferase, sulphotransferase and glyoxalase) were measured in the microsomal or cytosolic fractions obtained from ileum and colon mucosa. The activity in the ileum was higher than in the colon for NADPH cytochrome c reductase (p less than 0.05) and cytosolic epoxide hydrolase (p less than 0.001) (phase I enzymes), and glutathionetransferase (p less than 0.02), sulphotransferase (p less than 0.05) and glyoxalase (p less than 0.02) (phase II enzymes). The other enzymes had similar activities in two mucosa. The distribution pattern of drug metabolizing enzymes cannot be considered as a single pattern in human ileum and colon because of the observed enzyme-dependent differences.