The major virulence factor produced by the bacterium Bacillus thuringiensis (Bt) is a pore-forming toxin called crystal (Cry) toxin, which targets and kills insects and nematodes. To understand how this bacterial toxin interacts with its invertebrate hosts, a genetic screen in C. elegans for nematodes resistant to Bt toxin was carried out. Four of the five genes that mutated to toxin resistance encode glycosyltransferases. These genes were found to participate in the biosynthesis of C. elegans glycosphingolipids. These glycolipids in turn were shown to directly bind Bt toxin. Thus, resistance to Bt toxin in C. elegans can develop as a result of loss of glycolipid receptors for the toxin. Here we describe the isolation of Bt toxin resistance mutants in C. elegans, isolation of C. elegans glycolipids, and their separation by thin-layer chromatography, overlay assays to demonstrate direct binding of Bt toxin to glycolipids, and the purification of specific C. elegans glycolipid species.