Caenorhabditis elegans has close homologs or orthologs of most mammalian (RGS) and G proteins, and mutants for all the RGS and G-protein genes of C. elegans have been generated. C. elegans RGS proteins can be matched to the specific Galpha proteins they regulate in vivo by comparing the defects in animals lacking or transgenically overexpressing an RGS protein with defects in a specific Galpha mutant. Transgenic expression of mutated RGS proteins or subdomains in C. elegans has also been used to carry out structure/function studies of RGS proteins. We propose that similar strategies can be used to understand the function of RGS proteins from other organisms by expressing them in C. elegans. This article describes general considerations regarding such experiments and provides detailed protocols for quantitatively measuring G-protein signaling phenotypes in C. elegans.