Technical Abstract: Resistance in insects to Bacillus thuringiensis (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 (Fabricius) was initiated in 1996 by 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 Cry I A(c) protein nexpressed in transgenic cotton). Monitoring results showed no shifts in baseline susceptibility levels of biological insecticides (and thus, B.t. cotton), but data are very preliminary, especially in TBW because of low numbers in the 1996 season. Resistance monitoring will expand and continue in 1997.