Chemical carcinogens are generally activated enzymatically to electrophiles that form covalently bound carcinogen-DNA adducts. Detoxifying enzymes are competing with the activating enzymes for these procarcinogenic chemical substrates. Wide person-to-person variations in these two types of enzymatic activities are found. Repair rates of DNA damage caused by carcinogens also vary among individuals. These interindividual differences in the metabolism of chemical carcinogens and repair rates of carcinogen-induced DNA damage reflect acquired and inherited host factors that may influence an individual's risk for development of cancer.