The production of transgenic Bt cotton (NuCotn® 33B) in 1996 in southeast central Louisiana was observed to have been affected by several insect pests, including unusually heavy cotton bollworm (Helicoverpa zea) (CBW) populations. Survival of CBW larvae age 1-4 days feeding on NuCotn®33B bolls 1½ inches or younger far exceeded presumed economic injury thresholds for boll damage. Therefore, synthetic pyrethroid applications were required in order to prevent damage to NuCotn®33B. Conventional varieties sustained less injury initially since ordinary treatment thresholds triggered pyrethroid application prior to larval injury to bolls. Plant agronomic characteristics and weather conditions also contributed to varying yield outcomes, which trended much lower than expectations, in spite of intense cultural and pest management inputs.