Laboratory toxicity studies were conducted to determine the subacute effects of Bt Cry1Ab corn leaf material on nontarget soil organisms. Survival and growth were measured for an earthworm, Eisenia fetida Savigny, and survival and reproduction were measured for a springtail, Folsomia candida Willem. The organisms were provided leaf material of two Bt11 corn varieties, two Mon810 corn varieties, and the isolines of each, in a soil system and monitored for 28 d. An assay control treatment of an optimal food and a reference control treatment, using the herbicide pendimethalin, were used to provide a context for the observed results. Basic nutritional data of protein, fat, and sugar content were analyzed for each food type. Greater growth was observed for E. fetida in two Bt varieties, Bt11 90-d and Mon810 108-d, compared with their isolines. F. candida receiving Bt11 90-d isoline material had more offspring compared with those in the corresponding Bt line, but no other pairs were different. Time to reproduction of F. candida was only affected by the reference control treatment. Both protein and sugar content were found to correlate significantly with growth for E. fetida, but the nutritional parameters were not found to correlate with the effects observed for F. candida. These results indicate that there is little direct hazard from Bt corn leaf material to E. fetida and F. candida but that differences in nutritional parameters of the Bt lines and the isolines may lead to differences in the effects on nontarget organisms.