Studies have shown that there are many substances that can interfere with the actions of carcinogens and mutagens. Porphyrins, which often are constituents of diet, are a class of such inhibitors. Hemin can inhibit selectively the activity of mutagens having polycyclic structures by forming complexes with them. These effects were found with the use of bacterial assays and also by in vitro chemical experiments. A survey of porphyrins for similar effects has been done in our laboratory and it was found that chlorophyll and chlorophyllin act like hemin. These green pigments are antimutagenic in Salmonella and in Drosophila. Work from other laboratories also has supported the antimutagenic character of chlorophyllin. The possibility of modifying human exposure to carcinogens by use of these porphyrins is discussed. A porphyrin-like molecule, copper phthalocyanine trisulfonate, has been shown to have strong affinity to polycyclic compounds. Blue cotton, a cotton preparation bearing this blue pigment as a covalently bound ligand, has been demonstrated to be an adsorbent useful for isolating heterocyclic amines from food and other materials.