The possibility that the alpha-adrenergic agonist clonidine can act as a reinforcing agent was investigated using the conditioned place preference paradigm. Using two different variants of this method we were able to demonstrate reinforcing properties of clonidine at doses of 200 and 400 micrograms/kg. These results are consistent with those obtained by other investigators using the self-administration technique, and support the view that adrenergic mechanisms may be involved in reinforcement.