We investigated the chemotaxis of the nematode Caenorhabditis elegans toward cycloheximide, denatonium benzoate, 6-n-propyl-2-thiouracil, and quinine hydrochloride. Interestingly, C, elegans was strongly attracted to cycloheximide, while avoiding quinine hydrochloride. This is the first report thus far to describe the chemotactic responses of C. elegans toward bitter tastants for humans.