The cataleptic response to various doses of the dopamine-receptor antagonist spiperone and the cholinergic agonist pilocarpine was investigated in rats of different ages. Spiperone produced catalepsy in rats 1, 5 and 10 days old, and also in adults. Pilocarpine produced catalepsy in 15- and 20-day old rats, as well as in adults, but not in 10-day old animals. These results suggest that dopaminergic neurons involved in catalepsy are already functional in neonates. Cholinergic substrates of catalepsy, on the other hand, appear to reach functional maturity after the second week of life.