The effects of the noradrenergic neurotoxin DSP4 on imprinting in domestic chicks were investigated. Chicks received either DSP4 or distilled water and were trained 60 hr after hatching by exposing them to either a rotating red box or a stuffed jungle fowl. Noradrenaline concentration was determined in Wulst and medial and basal forebrain samples. The medial forebrain sample comprised mainly the intermediate part of the medial hyperstriatum ventrale, a region previously shown to be intimately involved in imprinting. The DSP4 treatment reduced forebrain noradrenaline levels by about 65%. DSP4 profoundly impaired imprinting in box-trained chicks but not in fowl-trained chicks. In box-trained chicks, the strength of imprinting was positively correlated with noradrenaline concentration in both medial and basal forebrain samples. It is suggested on the basis of these and previous studies that some of the neural structures and mechanisms involved in imprinting on the fowl differ from those involved in imprinting on the box.