The decomposition of residue from three genetically-modified (GM) corn varieties expressing one or more Bt endotoxins was compared to that from a variety with the unmodified base genetics. The corn hybrids were (i) DKC60-16 (Yieldguard Corn Borer), (ii) DKC60-12 (Yieldguard Corn Rootworm), (iii) DKC60-14 (Yieldguard Plus = stacked), and (iv) DKC60-15 (base genetics). The residue was collected in November, 2004 from experimental plots of each variety cultivated under identical no-till conditions. There was little pressure from corn borers or rootworm reported at this site. The decomposition rates of dried, chopped stalks and leaves were evaluated with the litterbag method using 2 mm mesh poly bags. Nine bags per variety were buried in each of 7 randomly-assigned blocks in a sandy-clay loam soil plot where spring wheat had been recently harvested and the residue incorporated by chisel plow. The top of the bag was buried 5 cm below the soil surface. The first block was excavated when the ground thawed at the end of March. The percent of residue on a dry weight basis (average of 9 replicates with 1 standard deviation in parentheses) decomposed over winter was 30.6 (±4.8) for the base genetics, 31.7 (±2.3) for Yieldguard Corn Borer, 28.4 (±2.9) for Yieldguard Corn Rootworm, and 27.8 (±1.9) for Yieldguard Plus. There was no significant difference in residue decomposition rates after this initial four month period or after seven months following burial (late June), despite measured differences among the varieties in the lignin content of the initial residue. The remaining blocks of litter bags will be periodically excavated to calculate annual decomposition rates. The measurement of residue decomposition rates in the field will assist in resolving conflicting reports on GM corn residue composition and recalcitrance and frame potential implications with respect to carbon budgets and farming practices.