Avoidance conditioning and the method of limits were used to measure absolute auditory thresholds, masked thresholds, and critical ratios in 4 parakeets. The same procedure was then used to study frequency difference limens in 6 additional animals. The power spectrum and "constancy of intonation" of the parakeet call were also measured and related to the absolute and differential frequency sensitivity. The mechanism of frequency analysis in the parakeet ear was considered in relation to the present results and to the anatomical and functional differences between the avian and mammalian auditory systems.