Territorial males of the Brilliant-thighed dart-poison frog, Epipedobates femoralis, are known to present stereotypic phonotactic responses to the playback of conspecific and synthetic calls. Fixed site attachment and a long calling period within an environment of little microclimatic changes render this terrestrial and diurnal pan-Amazonian species a rewarding subject for frog bioacoustics. In field experiments at Aratai, French Guiana, we tested whether the prominent frequency modulation of the advertisement call notes is critical for eliciting phonotactic response. Substitution of the natural upward sweep by either a pure tone within the species frequency range or a reverse sweep did not alter the males’ phonotactic behavior. Playbacks with advertisement calls embedded in high levels of either low-pass or high-pass masking noise designed to saturate either the amphibian (AP) or basilar papilla (BP) showed that male phonotactic behavior in this species is subserved by activation of the BP rather than the AP of the inner ear. [Work supported by grants from Austrian Science Foundation P 11565, P 15345 (WH), and NIH (PMN).]