AbstractFour carotenoids, canthaxanthin,β‐carotene, 8'‐apo‐β‐carotenal, and 8'‐apo‐β‐carotene methylester were tested for their ability to suppress the mutagenicity of 1‐methyl‐3‐nitro‐1‐nitrosoguanidine and benzo[a]pyrene (BP) in Salmonella typhimurium tester strain TA 100. The anticarcinogenic efficacy of the four carotenoids was further assessed in the BP‐induced forestomach tumor model in female Swiss mice. The effect of dietary palm oil was also examined in BP‐induced neoplasia in the female Haffkine Swiss mouse strain. Canthaxanthin,ß‐carotene, 8'‐apo‐ß‐carotenal, and 8'‐apo‐ß‐carotene methylester showed a dose‐dependent decrease in the mutagenicity compared with 1‐methyl‐3‐nitro‐1‐nitrosoguanidine and BP in strain TA 100. In the BP‐induced forestomach tumor model, all four carotenoids showed a similar significant anticarcinogenic effect. Dietary administration of palm oil showed a dose‐dependent antitumor activity in the animals. Our results show that the intrinsic antimutagenic and anticarcinogenic properties of the carotenoids are not significantly influenced by their conversion to vitamin A.