In 1995, ears of a experimental inbred (CG59-2) containing asynthetic Bacillus thuringiensis Cry IA(b) gene driven byPEPC, pith and pollen promoters and artificially infested withOstrinia nubilalis (Hübner) larvae in small plotstudies were free from insect damage, whereas 40–50% of thecorresponding non-Bt inbred ears were damaged. Bt inbred ears that wereinoculated with Aspergillus flavus Link and Fusariumproliferatum T. Matsushima (Nirenberg) or exposed to natural moldinoculum after infestation with O. nubilalis were free ofvisible signs of mold, as compared with ≈30–40% of the non-Bt earssimilarly treated. Results in 1996 using the same inbred with a singleallele dose of the Bt gene showed similar trends. Mean total fumonisinlevels for non-Bt versus Bt inbred ears were not significantlydifferent (2.8 versus 0.8 ppm, respectively) in 1996. In paired hybridstudies run in 0.4-ha (1-acre) fields, an event 176 Bt hybrid hadsignificantly lower amounts of damage and signs of Fusariumspp. mold, but not fumonisin, compared with a corresponding non-Bthybrid from 1996 to 1998. However, two hybrid pairs that containedeither MON810 or Bt11 constructs examined in similar fields at the samesite had lower levels of fumonisin in both 1997 (30- to 40-fold) and1998. High intrafield variability in insect infestation and presence ofHelicoverpa zea (Boddie) in Bt hybrids was apparentlyresponsible for fewer significant differences in fumonisin levels in1998. Similar trends for all three hybrid pairs were noted in smallplot trials at another site. Incidence of other ear pests or insectpredators varied as much among non-Bt hybrids as they did for Bt/non-Bthybrid pairs.