Allylnitrile, crotononitrile and 2-pentenenitrile induce this behavioral syndrome, which includes persistent random circling, head twitching and backward running. The effects of neurotropic agents, with a selectivity for the alpha 1 or alpha 2 adrenoceptor, were examined on the nitrile-induced behavioral abnormalities. The alpha 1 agonist phenylephrine, the alpha 2 agonist clonidine and the alpha 1 antagonist prazosin, inhibited the behavioral syndrome induced by each nitrile, while the alpha 2 antagonist yohimbine had no effect. These results suggest that the noradrenergic system may be involved in the manifestation of the syndrome. Furthermore, a tonic noradrenergic influence on subcortical systems may be required for the syndrome to occur.