An attempt was made to study the effects of a tranquilizer (metoserpate hydrochloride), specifically designed for poultry, on the neonatal approach response of domestic chicks. Acquisition of this response was accomplished in a straight alley on birds ranging in age from 24 to 120 hours old. Testing of this response was done when all birds were 144 hours old under a no-drug condition. At 168 hours of age all subjects were subjected to extinction procedures. The strength of the response was measured in terms of latency to start as well as time spent traversing the alley. Resistance to extinction was measured in terms of the latencies mentioned above as well as number of trials to extinction. The results of the present study show a peak in imprinting susceptibility between 72 and 96 hours after hatching. The tranquilizer had a traditional interference effect except for those birds exposed on Day 3 while the injection control procedure had an enhancement effect on birds treated on Days 4 and 5. In addition, there were no differences observed during extinction between groups. / Master of Science