The effects of the chitin synthesis inhibitor triflumuron, 2-chloro-N- [[[4-(trifluoromethoxy)phenyl]amino]carbonyl]benzamide, on the housefly, Musca domestica Linnaeus were examined in the laboratory. A dose of 1 fig of triflumuron applied topically to adult females of M. domestica resulted in egg hatch inhibition greater than 95%. At doses below 1 ug applied topically to adult females, subsequent hatched larvae were also highly sensitive to triflumuron; 0.5 |Xg applied topically produced 25% inhibition of egg hatch, but of the larvae that eclosed, only 20% survived to pupation. Hence, a dose of 0.5 fig applied to adults gave a total mortality of 85%. The effects of a single topical application of triflumuron declined over time in a dose dependent manner. After a dose of 1 \xg, < 5% of the first egg batch hatched, however, after 14 days egg hatch had risen to > 90%. Topically applied triflumuron was most effective in inhibiting egg hatch when applied to females less than 3 days old. After 60 min tarsal contact with 20% triflumuron suspension concentrate on poly cotton cloth, 100% egg hatch inhibition was maintained for up to 1 week. Lower contact times, or triflumuron concentrations, gave lower percentage mortalities. The results suggest that triflumuron has considerable potential as a control agent for incorporation into autosterilizing devices for housefly control. However, further work is required to develop delivery systems capable of transferring an effective dose to females under field conditions.