Auditory sensitivity in 6 bullfrog tadpoles (Rana catesbeiana) was investi- gated electrophysiologically. Tonal stimulus intensities that elicited a standard sensory potential of 0.1 ,v in the inner ear showed a response range from 100 Hz to 4000 Hz with maximum sensitivity near one dyne/cm2 (0.1 N/m2) in the lower portion of the range. These potentials also indicated that tadpoles lack the place mechanism of adult frogs. * * * While many articles have appeared assessing hearing in fishes and adult amphibians, especially frogs, no work on larval amphibians has been reported. Larval amphibians are particularly interesting because their hearing apparatus with columellar connections between an internal air bladder and the inner ear parallels that in ostariophysian fishes with their Weberian ossicles. At metamorphosis the frog ear becomes more typically like that of other terrestrial vertebrates with an external ear drum and a columellar connection to the inner ear. The roles of the round and oval windows of the inner ear even reverse during metamorphosis (van Bergeijk, 1967). Thus the lack of data on the development of auditory sensitivity in amphibian larvae leaves a considerable hiatus in the understanding of vertebrate hearing in general. The present study employs electrophysiological techniques to explore the auditory sensitivity of the bullfrog (Rana catesbeiana) tadpole.