Inter- and intraspecific variation in alarm calls were compared for two species of free-ranging capuchin monkey: the wedge-capped capuchin (Cebus olivaceus) and the white-faced capuchin (Cebus capuchinus). Alarm calls in each case were made in the presence of the same predator, a boa constrictor. Vocalizations (n=40) were compared for commonly examined acoustic parameters (e.g., signal duration, frequency, and amplitude variables), as well as for vocal features found to be acoustic cues to the monkeys [e.g., bandwidth of dominant formant; change in frequency of the dominant formant (see Norris, 4aAB3)]. Additionally, correlations of spectrograms were performed using CANARY. Interspecific variability was found to be significantly greater than intraspecific variability for signal duration (F=45.30;p<0.0001), maximum frequency (F=8.52; p<0.0059), and formant number (F=10.32;p<0.0027). However, interspecific variability of calls was not significant for any of the acoustic parameters found to be used as perceptual cues for the two species. The evolutionary and ecological significance of these findings will be discussed.