Caenorhabditis elegans is well suited for toxicological studies owing to its established biology, short generation time, large brood size, and readily scorable life traits. Quantitative parameters of C. elegans that can be assayed include growth, size, progeny production, behavior, and mortality. Qualitative parameters of toxicity, such as changes in appearance or movement, can also be determined. This chapter describes four assays we have used for analyzing the toxic effects of Bacillus thuringiensis crystal proteins toward C. elegans. The assays are quantitative growth measurement, brood size measurement, and determination of lethal concentration, as well as a qualitative health assay based on worm appearance. Although these assays are described for crystal proteins, the approaches are suited for the studies of other toxins with C. elegans.