The structure-activity relationships of 25 triorganotin(IV) compounds were studied using the 4th instar A. aegypti larvae of the susceptible Liverpool Red-eye strain. The LC50 values of these compounds were compared with those of Malathion, DDT and Temephos. Maximal activities were obtained with tritolyltin chloride and its complexes with triphenyl-phosphine oxide and pyridine N-oxide, dimethyloctyltin- and diethyloctyltin acetates and tributyltin sucrose phthalate. A limited number of the triorganotin compounds was also tested with observed high activity against the 4th instar larvae of a local DDT-tolerant strain and against the 2nd instar larvae and adults of the susceptible strain. Delayed effect studies with both 2nd and 4th instar larvae showed high post-treatment mortality for the latter and, among the range of active compounds, the methyl- and aryltin compounds, in particular, were also found to exhibit high residual activities (100% kill) in laboratory tests conducted up to 10 weeks.