Taste sensitivity in mice and its strain variation were studied by examining integrated responses and single fiber discharges of the chorda tympani nerve to various taste stimuli in the 3 different strains of mice (BALB, C3H and C57BL mice). A comparison among integrated responses of the 3 strains demonstrated that C57BL mice possess the highest sensitivity to sucrose and the lowest to acids, whereas the opposite is true for BALB mice. These 3 strains of mice commonly possess higher sensitivity to divalent chloride salts than to NaCl. Measures of the breadth of responsiveness showed that single fibers of all 3 strains of mice are relatively more narrowly tuned to taste stimuli than those of rats and hamsters, although the specificity of fibers tends to be greater in the order of C57BL greater than C3H greater than BALB mice. A cluster analysis of fibers demonstrated that two distinct fiber types, a sweet- and Na-type, commonly exist in all 3 strains of mice. The most clear strain difference was found in the sensitivity to D-phenylalanine, which produced good responses in 'sweet-type' fibers of C57BL mice but not in those of C3H and BALB mice. This suggests the possibility that D-phenylalanine has a taste to C57BL mice that is similar to that of sucrose and that it tastes different to C3H and BALB mice.