We examined how male and female túngara frogs, Physalaemus pustulosus, respond to variation in the frequency spectrum of the chuck component of the advertisement call. We varied chuck frequency in two different ways. In the fixed frequency series, the sequence of calls within each series had chucks of the same dominant frequency. Different fixed-frequency series had chucks of different dominant frequencies designated as high, high–medium, medium, medium–low, or low frequency relative to variation in the test population. In the second varying frequency series, the sequence of calls varied in the chuck's dominant frequency such that the individual series had the same average frequencies as the high, high–medium, medium, medium–low, and low fixed-frequency experiments. Both males and females tended to respond more to lower-frequency chucks. The responses of both sexes to the same mean chuck frequency was similar to the fixed- and varying-frequency series of chucks.