1. Synthetic calls with a waveform periodicity of 300/sec and a bimodal spectrum attracted female green treefrogs as effectively as natural calls.
2. Effectiveness was markedly reduced if the relative amplitude of the two spectral peaks differed by as little as 10 dB.
3. Optimal frequency bands were 900-1100 Hz in the low range and 2700-3300 Hz in the high.
4. Addition of components at 1800 and 2100 Hz rendered the call less attractive.
5. In the absence of a bimodal stimulus, most females responded to a call containing a single spectral peak in the high or low range.
6. Mating call recognition in the green treefrog is compared with that in the bullfrog.