The upper frequency range varies within each species and even within the calls of one individual. _Smilisca phaeota_ has the lowest upper frequencies; no calls ranged above 4400 cycles per second (cps.), and half of the calls never exceeded 3000 cps. _Smilisca cyanosticta_ produces calls in which the upper frequency is below 7000 cps. and usually below 6000 cps. Likewise, _S. puma_ produces calls that are below 7000 cps., whereas _S. sila_ has frequencies of up to 8400 cps. In both _S. baudini_ and _S. sordida_, the highest frequencies attained are about 9100 cps. Variation in the highest frequencies in a series of consecutive calls by one individual frog was noted in all species. Such variation is especially prevalent in _S. puma_; for example one individual (KU 87771; Tape No. 376) recorded at a temperature of 24 deg. C. at 7.5 kilometers west of Puerto Viejo, Heredia Province, Costa Rica, on July 31, 1964, produced three consecutive primary notes having upper frequencies of about 6000, 4000, and 4000 cps., respectively. Apparently in a given species the production of the higher frequencies in some notes and not in others is correlated with the amount of distention of the vocal sac and is not dependent upon the structure or tension of the vocal cords. Although the dominant frequency in _S. sordida_ is lower than that in _S. baudini_ and _S. cyanosticta_, the call of the former is audibly higher-pitched. This is due primarily to the emphasis on certain harmonics at a high frequency (sometimes as high as 9000 cps.) in _S. sordida_, whereas in _S. baudini_ and other species, if harmonics are present at those frequencies, they are not emphasized. The fundamental frequencies are as low as 90 cps. in _S. sila_ and _S. sordida_ and as high as 200 cps. in _S. puma_ (Table 8). The fundamental frequency seemingly is relatively unimportant in determining the general pitch of the call, a characteristic most dependent on the dominant frequency and emphasized harmonics in the higher-frequency spectrum. In none of the species is the fundamental the dominant frequency. In the low-pitched call of _S. phaeota_ the dominant frequency is the third harmonic (the second harmonic above the fundamental frequency, which is the first harmonic). In all other species a much higher harmonic is dominant; for examples, in _S. cyanosticta_ harmonics from 10 to 15 are dominant; in _S. baudini_, 15-19; and _S. sila_, 20-30.