The hypothesis that aggression is affected by varying the affective value of the imprinted stimulus was tested with 12 Bardrock chicks. The affective value was defined as a hypothetical response of the animal which was inferred from observable events such as distress calls and flight responses. An aggressive response was defined as an imprinted bird's peck at a socialized bird. In order to vary the value of the imprinted stimulus, different shock frequencies were paired with the simultaneous withdrawal of the imprinted stimulus. The difference in aggressive responses between the experimental and control S s was significant (p less than or equal to .01). The present experiment suggests that only moderate levels of aversive stimulation when added to the imprinting process served to maximize both imprinting and aggression. Shock intensities either above or below this level resulted in reduced aggression--in the former case because of interference due to overstimulation, in the latter because of incomplete excitation.