Field com, genetically engineered to produce a protein derived from Bacillus thuringiensis kurstaki strain HD-1, was evaluated for its effects on larva of the noctuid species Agrotis ipsilon (Hufnagel), Papaipema nebris (Geunee), Pseudaletia unipuncta (Haworth), and Helicoverpa zea (Boddie). No B. thuringiensis corn effects were observed on larval survival, pupal weight, or days to adult emergence for A. ipsilon or P. nebris; however, P. unipuncta reared on B. thuringiensis leaf extract were 0.068 g lighter in pupal weights, delayed for 8 d in preimaginal development (from 33 to 41 d), and showed trends for 11-25% lower survival. Reduced survival and a 4-d delay in preimaginal development also was observed for H. zea reared on B. thuringiensis -treated meridic diet. In 1994 and 1995, transgenic B. thuringiensis com and non- B. thuringiensis com seed was planted under field conditions. Eighty B. thuringiensis and non- B. thuringiensis plants were artificially infested with early instars of the 4 noctuid species, then evaluated for damage (leaf feeding, stalk cutting, ear-tip feeding). There were no differences between B. thuringiensis and non- B. thuringiensis com damage caused by A. ipsilon. In 1994, P. nebris caused significantly less leaf-feeding damage to B. thuringiensis corn than non- B. thuringiensis com. In addition, P. unipuncta and H. zea caused significantly less damage to B. thuringiensis com leaves. H. zea survived on and caused damage to B. thuringiensis com ears, and even though there were fewer ears damaged, there was no difference in the number of live larvae per plant on B. thuringiensis com than on non- B. thuringiensis com.