Eighteen compounds structurally related to the mutagenic carcinogen vinyl chloride have been tested for mutagenicity in five strains of Salmonella typhimurium. Acrolein, acrolein diethylacetal, acrylonitrile, allyl alcohol, allyl bromide, crotonaldehyde, crotyl alcohol, and vinyl bromide were mutagenic with one or more strains; acrolein bisulfite, acrolein oxime, acrylamide, acrylic acid, allylamine, trans-cinnamaldehyde, trans-cinnamic acid, crotonic acid, methyl methacrylate, and vinyl acetate were not mutagenic. The mutagenicity tests were performed both without and with activation by rat and hamster liver microsomal preparations (S9). All compounds were tested in the plate incorporation and/or liquid preincubation tests except vinyl bromide, which was tested as a gas.