Rats were trained in 4 consecutive trials to obtain a liquid reward in a labyrinth system. Drugs were given s.c. 2-4 hours before each trial, and starting time (ST), running time (RT) and number of errors (NE) were recorded on the fourth trial. Hydergine reduced NE independently of its effect on ST and RT. Dihydroergocristine and dihydroergocornine prolonged ST, dihydro-alpha-ergokryptine reduced NE whilst dihydro-beta-ergokryptine did not induce any significant effect on the three parameters. These results demonstrated that none of the Hydergine components exerts a similar effect to that of Hydergine in this model. It is also known that Hydergine influences neurotransmitters like serotonin, dopamine, noradrenaline and acetylcholine in vivo and in vitro. Therefore, the effects of Hydergine on cognitive functions in rats appear to be the consequence of its different actions on the cerebral transmission.