Abstract: L-Tryptophan is applied to foodstuff to prevent the development of mutagens/carcinogens. Before the cooking of a foodstuff such as hamburger, L-Tryptophan is applied to the surfaces thereof to inhibit, for example, the generation of IQ type carcinogens. The L-Tryptophan can be sprinkled on the surface of the foodstuff or incorporated into a sauce which is applied to the foodstuff or put into solution in water or the like.Other non-toxic indoles such as L-proline have identical properties in specifically blocking the formation of heterocyclic amino type mutagens and carcinogens, as do mixtures of L-tryptophan and L-proline.