Seventy-nine hamster and 45 squirrel monkey chorda tympani nerve fibers were classified as to which of four basic taste compounds: sucrose, sodium chloride, hydrochloric acid, or quinine hydrochloride elicited the largest response. Knowing whether the fiber belonged in the sucrose-best, salt-best, or acid-best group and the species from which it was sampled allowed prediction of the relative effectiveness of the other three basic stimuli, as well as the effectiveness of fructose and ammonium chloride for most fibers. Thus, mammalian taste nerve fibers can be typed according to their collection of sensitivites.