The present study was undertaken to investigate the effects of a single (24 h) and repeated (7 days) doses of deltamethrin (10 rngikg body weight daily) on hepatic drug metabolizing enzymes. The hepatic content of microsomal protein, cytochrome P450 and b5. activities of NADPH cytochrome C reductase, amidopyrine N—demethylase. aniline-4shydroxylase. glutathion S-transeferase and the level of thiobarbituric acid reactive substances (TEARS) were determined. The obtained results indicated that a single dose of deltamethrin had no significant effect on hepatic microsomal proteins, cytochrome b5, amidopyn‘ne N-demethylase, aniline-4- hydroxylase, or TEARS. However, it significantly decreased (p < 0.05) the activity of cytochrome P450. and increased the activities of NADPH cytochrome C reductase {p < 0.001) and glutathion S-transeferase (pit-0.05). Repeated doses of deltamethrin significantly decreased the activities of hepatic microsomal proteins (ps0.05) and amidopyrine N-demethylase (p¢0.001), and increased the activities (Ps0.01) of other studied enzymes. The obtained results indicated that single and repeated doses of deltamethrin had marked effects on hepatic drug metabolizing enzymes.