Single units from the auditory nerve of frogs and toads have their receptor cells located in two separate sensory organs that provide disjoint frequency ranges. The amphibian papilla (ap) provides units with characteristic frequency (CF) in the low- and mid-frequency regions and the basilar papilla (bp) provides units with high CF. There are gross differences in both the mechanical design and innervation patterns of the two organs, so that one might expect discharge properties for units with different CF to differ in many respects. However, there have been few reports of response attributes that correlate strongly with CF for units in the mid- and high-CF regions. Measurements of automated tuning curves from 250 units in Rana pipiens show that W10 dB, the bandwidth of the tuning curve measured 10 dB above CF threshold, is consistently larger for high-CF units than for low- and mid-frequency units. When units are classified into three groups by an objective statistical method using only CF and W10 dB measurements, the groups appear to correspond reasonably well with the low-, mid-, and high-frequency categories identified in many other studies.