In 1997 cotton growers in South Carolina planted about 30% of their 291,000 acres to Bollgard varieties (Bt varieties), mostly DPL NUCOTN 33B. Statewide field surveys and grower comments in 1996 showed that the Bt varieties had provided good control of bollworms, but farmers still treated them with pyrethroids, an average of more than one application per season. Furthermore in 1996 a number of researchers, extension workers and consultants in different states, voiced the opinion that one or two pyrethroid applications to Bt cotton increased yields over untreated Bt cotton. This study was conducted in 1997 at 10 different on-farm locations to compare DPL 33B treated with one or two pyrethroid applications, with DPL 33B that was untreated, and with DPL 5415 treated conventionally.