Resistance in insects to Bacillus thuringiensis Berliner (B.t.) delta endotoxin proteins has recently received considerable interest both nationally and internationally for three primary reasons: (1) unprecedented interest on the part of the environmental community and organic producers; (2) the recent registration and deployment of transgenic plants in many countries; and (3) laboratory and field resistance to B.t. in 10-12 insect species. Preliminary B.t. resistance monitoring in cotton in populations of cotton bollworm (CBW), Helicoverpa zea (Boddie), and tobacco budworm (TBW), Heliothis virescens (F.) was initiated in 1996 by (1) subjecting 23 different populations of these insects collected in Arkansas, Mississippi, Oklahoma, and Texas to field doses of MVP® II biological insecticide in spray chamber bioassays (the toxic protein in MVP® II is the closest in toxicological properties of all B.t. insecticides to the CryIA(c) protein expressed in transgenic cotton), and (2) subjecting larvae of CBW and TBW from 3 sites in Mississippi to B.t. delta endotoxin to select the optimum diagnostic dose in rearing diet. Preliminary monitoring results from both methods showed no shifts in baseline susceptibility levels of bollworm and budworm to B.t. insecticide (and by inference to B.t. cotton). These studies will continue and expand in 1997.