Cry1Ab protein expressed in vivo must be quantified before use in bioassays for determination of its toxicity to insects. However, it is difficult to find reliable methods of quantification, especially with unpurified samples. We compared two methods to quantify unpurified Cry1Ab isolated from Escherichia coli (JM103): 1) Densitometric quantification using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with Coomassie blue staining; and 2) Enzyme-Linked Immunosorbent Assay (ELISA). Both methods were validated with bioassays of Ostrinia nubilalis (Lepidoptera: Crambidae) neonates. The susceptibility of neonates to unpurified and purified Cry1Ab toxins was determined by exposure to different concentrations of Cry1Ab applied onto the surface of artificial diet. These results are important to validation and standardization of resistance monitoring efforts.