The mutagenicity of a series of potassium alkanediazotates in the Ames assay was studied. These compounds were isolated as solids and are soluble in dimethyl sulfoxide. Upon addition to water, they form diazohydroxides (which are postulated intermediates in the decomposition of alpha-hydroxylated nitrosamines). The diazohydroxides decompose to electrophilic intermediates which may react with macromolecules or water. In the Ames assay, potassium diazotates produced his+ revertants in Salmonella typhimurium strains TA 100 and TA 1535 but not in strains TA 98, TA 1537, or TA 1538. Methane, methane-d3, ethane, propane, and phenylmethanediazotates were mutagenic in strain TA 100, and all diazotates with the exception of phenylmethanediazotate, produced revertants in TA 1535. The order of mutagenic potency of these compounds was: methane approximately equal to methane-d3 greater than ethane, greater than phenylmethane (TA 100) greater than propane greater than phenylmethane (TA 1535) = 0. All diazotates were direct-acting mutagens and produced revertants even when no liver 9000 X g supernatant (S9) fractions were present. S9 fractions inhibited the mutagenicity of potassium diazotates, and equivalent concentrations of S9 fractions (3 mg protein per plate) from either rat or hamster liver, whether induced or not, were equally effective. Bovine serum albumin was not as effective as S9 fractions in inhibiting diazotate mutagenesis, but heat-inactivated (70 degrees for 20 min) S9 fractions were as inhibitory of methanediazotate mutagenicity as native S9 fractions were at low protein concentrations. The half-lives of mutagenicity of methane- and ethanediazotates in aqueous solutions were identical (less than or equal to 15 sec); after less than 2 min in solution, these diazotates were rendered completely inactive. The implications of these studies for mechanisms of nitrosamine action and the use of potassium alkanediazotates as model compounds for activated nitrosamines are discussed.