A study was undertaken to assay the various phase I and phase II drug metabolising enzymes in zinc deficiency. Male weanling Fischer rats were subjected to zinc deficiency for a period of 7 weeks. Zinc levels in the control and deficient diets were 30 mg and 1.1 mg/kg diet, respectively. At the end of the experimental period, the activities of various hepatic cytosolic and microsomal enzymes were estimated. It was observed that the activities of microsomal epoxide hydrolase (with benz(a)pyrene 4-5 oxide as substrate), uridine diphospho glucuronyl transferase (with 1-naphthol as substrate) and cytosolic glutathione-S-transferase (with chlorodinitrobenzene as substrate) were altered exclusively due to zinc deficiency. There was a change in the activities of the following enzymes, which could be due either to zinc deficiency and/or food restriction: 1) aryl hydrocarbon hydroxylase; 2) cytochrome b; 3) cytochrome c; and 4) cytochrome b5. Other enzymes studied, i.e., cytosolic epoxide hydrolases, microsomal EHSTO, and UDPGT testosterone were not different in the control and experimental groups. The results are discussed in relation to the activation of carcinogens and neoplastic formation in zinc deficiency.