Data from 2 field studies are summarized that evaluate insecticide use on non-transgenic and transgenic B.t. cotton. Effect of the insecticides on square and boll damage, aphid infestation, mite damage, and yield are reported. The newer insecticides Denim, Steward, and Tracer were generally found to provide effective caterpillar control. Karate and Leverage were not effective on tobacco budworm in 2000, but Asana and Leverage were effective on caterpillars (higher level of bollworms) in 2001. Transgenic B.t. cotton (DPL 33B) was highly effective on caterpillars in both years. Asana and Karate treated cotton contained higher levels of aphids, Leverage prevented aphid outbreaks, and Denim eliminated spider mites. Although not demonstrated statistically, DPL 33B cotton with and without insecticides and all insecticide treated non-transgenic (DPL 5415) cotton produced higher yields in the 2001 test (42-158 lint lb/acre) compared with untreated DPL 5415.