Chlordimeform (CDM), tested by topical application, was found to be toxic to both male and female tsetse with the maximum effect some 72 hr after treatment. Median lethal doses were approx. 0.4 μg/fly for unfed adult tsetse of both sexes, 100% mortality at 72 hr was achieved with 2 μg/fly. Mature fed females were less susceptible to chlordimeform, the median lethal dose for 72 hr being 12.5 μg/fly. High doses of chlordimeform depressed the weight of puparia from survivors, but had no effect upon fecundity. Sublethal doses caused a significant depression of feeding activity, but did not cause hyperactivity or disrupt fat body lipid reserves.