The relative toxicity to Musca domestica of certain aryl analogs of allethrin was evaluated by the turn-table method. The phenyl, benzyl, o-methoxybenzyl, p-methoxy-benzyl, and 3,4-methylenedioxybenzyl analogs of allethrin were, respectively, 34, 18, 7, 2, and 6% as toxic to house flies by this method as allethrin, and 95, 56, 18, 6, and 15% as toxic as pyrethrins. Substitution in the benzyl side chain was accompanied by considerable loss in toxicity with the 3 esters assayed. Substitution of the methylenedioxy group gave an ester 1/3 as toxic as the unsubstituted benzyl ester. Of the 2 isomers the ester with the methoxy group in the ortho position was about 3 times as toxic as the ester with the group in the para position but only about 1/3 as toxic as the unsubstituted analog. All the analogs possessed considerable knockdown value.