The effects of L-homoarginine, L-phenylalanine, L-phenylalanylglycylglycine and L-leucine and high temperatures on the alkaline phosphatases extracted from the skins, lungs, livers, kidneys, ovaries and small intestines of Rana nigromaculata, Rana japonica, Rana rugosa, Rana limnocharis, Rana catesbeiana, Rhacophorus schlegelii, Hyla arborea japonica, Bufo japonicus and Cynops pyrrhogaster were examined in order to confirm the differences in the stability of alkaline phosphatases to these inhibiting-agents. The alkaline phosphatases of the skins, lungs, livers, kidneys and ovaries from all species, as well as those of the small intestines from Rana nigromaculata, Rana japonica, Rana rugosa, Rana limnocharis, Rana catesbeiana and Rhacophorus schlegelii required nearly the same concentrations of inhibitors for 50 0nhibition, while the alkaline phosphatases of the small intestines from Hyla arborea japonica, Bufo japonicus and Cynops pyrrhogaster required remarkably higher concentrations of inhibitors for 50 0nhibition than the foregoing alkaline phosphatases. The alkaline phosphatases of all the organs from Rana limnocharis other than the small intestine were remarkably temperature-resistant.