The primary purpose of these experiments was to gather normative behavioral data regarding the ontogeny of responsiveness to sound in the chicken embryo. As a prerequisite, a sensitive ane accurate method for recording embryonic motility was developed (Experiment 1). By means of platinum electrodes inserted just beneath the shell membrane, potentials resulting from heartbeat and movement were recorded on a polygraph. The technique was found to be effective when applied to chick embryos 6 days and older. Correlations between visual observations of activity and the records produced by the electronic technique substantiated its accuracy. Behavioral responses of chick embryos (Stages 39-43) to acoustic stimulation (Experiment 2) were then recorded. High-intensity (115-dB SPL) tones of 400, 700, and 1400 Hz were used as stimuli. The earliest consistent responses were recorded from Stage 40 (ca. Days 14-15) subjects; the 700 and 1400 Hz tones produced statistically reliable inhibition of movement during the stimulus period compared with the post-stimulus period. Reliable increases in movement during the stimulus period were first recorded at Stage 42 (ca. Days 16-17) in response to 700 and 1400 Hz and at Stage 43 (ca. Days 17-18) in response to 400 Hz.