The overall aim of the research program is to study the various metabolic activation and inactivation processes involved in the carcinogenesis by various chemicals. It is known that N-hydroxylation of aromatic amines and amides is an activation step whereas ring-hydroxylation is an inactivation step. Similarly, oxidative dealkylation of dialkyl-nitrosamines and epoxidation of polycyclic aromatic hydrocarbons and aflatoxin B1 are also known to be activation processes. All of these metabolic steps are mediated via cytochrome P-450 present in the endoplasmic reticulum of liver and several other tissues of various animals. Our research program is concerned with solubilization, purification and characterization of these microsomal P-450 cytochromes. Reconstitution studies with these purified P-450 cytochromes for various carcinogen oxidations would enable us to know whether activation and inactivation processes are mediated via the same cytochrome P-450. Role of cytochrome b5, flavoproteins and lipids present in the endoplasmic reticulum is to be investigated in the metabolism of various carcinogens.