Dihydroergotoxine (DHET) improved the acquisition of a conditioned avoidance response in both young and old rats, although old animals, reached a lower percentage of conditioned responses than did young rats. DHET dose-dependently reduced locomotor activity in aged animals, while, in young rats, increasing doses caused a triphasic effect, inhibitory at low doses, stimulatory at intermediate doses and again inhibitory at high doses. In young rats, the stimulation of spontaneous movements by DHET was abolished by L-sulpiride; L-sulpiride had no effect in old animals. DHET treatment also potentiated both norepinephrine- and, to a greater extent, dopamine-stimulated frontal cortex adenylate cyclase activity, an effect more pronounced in young than in old rats. These data show that DHET effects both locomotor activity and active avoidance performance in young and aged rats, and modulates dopamine-sensitive adenylate cyclase activity.