Alkylation of DNA is regarded as a critical step involved in the mutagenic and carcinogenic action of N-nitroso compounds. The product distribution of DNA alkylation by N-nitroso compounds has been studied with several contributing factors in view. The theoretically computed values of these factors serve as clues to rationalise experimentally observed findings concerning this product distribution, and also allow for more generalised predictions that embrace a wider scope of application than the small list of compounds already studied experimentally. The relationship between product distribution and mutagenic and carcinogenic potency of N-nitroso compounds is briefly discussed.