Vapor toxicities of two prototype formate esters, ethylene glycol di-formate (EGDF) and heptyl formate, and the prototype heterobicyclic menthofuran were determined against laboratory-reared adult house flies, Musca domestica L. (Diptera: Muscidae). Toxicities were compared between house flies and other dipteran species tested previously. The organophosphate fumigant insecticide dichlorvos (DDVP) was used as a positive control. Although less toxic than DDVP, all three prototype compounds were toxic to house flies. Most toxic was menthofuran (LC50 = 3.70 mg/liter air), followed by EGDF (LC50 = 9.27 mg/liter air) and heptyl formate (LC50 = 32.62 mg/liter air). The toxicity of menthofuran when applied after piperonyl butoxide increased 1.5-fold. The toxicities of heptyl formate and EGDF when applied after S,S,S-tributyl phosphorotrithioate decreased by 1.5- and 2-folds, respectively. These results are slightly different from results obtained for other dipterans, further supporting previous hypotheses that toxicity may have some species specificity. Ceramic porous rods impregnated with heptyl formate were used to evaluate the effectiveness of controlled vapor release for a single dose of heptyl formate against house flies. Controlled vapor release ofheptyl formate can be used successfully to provide prolonged house fly mortality. Even though the prototype compounds did not exhibit toxicity as high as that of DDVP, their toxicities to dipterans, along with their reduced mammalian toxicities relative to DDVP, make them potential DDVP replacement candidates.