Chlorophyllin, the sodium and copper salt of chlorophyll, was tested for its ability to inhibit the mutagenic and carcinogenic properties of a variety of substances present in the natural and work environments. Extracts or concentrates of diesel emission particles, tobacco snuff, chewing tobacco, fried shredded pork, fried beef, airborne particles, cigarette smoke, coal dust, red grape juice, and red wine were evaluated for mutagenic activity using the Salmonella/mammalian microsome test. Salmonella- typhimurium (TA-98) with or without mammalian S9 mix was used, and after 2 days of incubation at 37 degrees-C the number of revertants per plate was counted. The mutagenic concentration of each extract was determined, and chlorophyllin was then tested to determine its ability to inhibit mutagenesis by each of the extracts. Chlorophyllin inhibited the mutagenic activity of each extract in a dose dependent manner. Complete inhibition was obtained against the mutagenic activity of extracts of airborne particles, cigarette smoke, fried shredded pork, and fried beef using concentrations of 1.25 milligrams (mg) of chlorophyllin per plate. Inhibition of 92 to 98 percent was obtained against extracts of diesel emission particles, coal dust, red grape juice, and red wine, but greater concentrations of chlorophyllin were required per plate. Concentrations of 10mg chlorophyllin per plate inhibited the mutagenic activity of tobacco snuff and chewing tobacco by 80 to 85 percent. The authors conclude that chlorophyllin inhibits the mutagenic activity of compounds belonging to a wide variety of chemical groups, including nitropyrenes, nitroso compounds, flavanoids, aromatic amines, and other polycyclic hydrocarbons. The mechanism of this inhibition is uncertain, but the authors suggest that it may be due to the ability of chlorophyllin to scavenge radicals or interact with the active groups of mutagens. The authors suggest that if it is proven to be non toxic and anticarcinogenic, it might prove beneficial to employ chlorophyllin as a food additive or dietary supplement to reduce the potential hazard of carcinogens in the environment.