The amounts of several drug-metabolizing enzymes in livers of Suncus murinus (suncus) were studied in comparison with rats. The content of cytochrome P450 in suncus was less than one third that seen in rats. Activities of glutathione S-transferase, UDP-glucuronyltransferase and arylhydroxycarbon hydroxylase in suncus were less than half those in rats. Activity of flavin-containing monooxygenase in suncus was 71% that of rats. Interestingly, N-acetyltransferase (NAT) activity in suncus liver cytosols was not detectable: no detectable activities were seen with aniline, p-aminobenzoic acid and p-amino-salicylic acid as substrates. We propose that suncus is a unique animal possibly lacking NAT in liver cytosol.