Grooming behavior in rats has so far been known to be induced mainly by dopamine agonists type D1. In order to explore the involvement of serotonine (5-HT) and its receptors in such a behavior, rats were exposed to two phases of treatment: to the serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), injected intraventricularly three days after birth, and to the serotonin partial agonist m-chlorophenylpiperazine (mCPP), administered in two dose levels, two months later. Grooming behavior was monitored immediately before and after the higher dose of mCPP, while brain levels of 5-HT and its major metabolite 5-HIAA were assayed one week after mCPP administration. It is documented that while a low dose of mCPP in the non-lesioned rats increased the grooming-time by 5.7-fold, the higher mCPP dose in the non-lesioned non-primed rats increased grooming behavior by 3.6-fold. The 5,7-DHT lesions caused a 6.7-fold increase in the non-primed rats, and a 4.2-fold increase in the primed ones. These increases were noticeable only in male rats. When a higher dose of mCPP followed its lower dose in the 5,7-DHT-lesioned rats, a 3.6-fold decrease was recorded only in the female rats. A 88% and 94% drop in 5-HT and 5-HIAA levels in the brain neostriatum of the 5,7-DHT-lesioned rats was noticed in both sexes, one week after mCPP administration. These findings are the first to demonstrate that the 5-HT2 partial agonist mCPP is capable of modifying grooming behavior, and that 5,7,-DHT brain lesions increase basal grooming time, suggesting that 5-HT neurons and receptors are involved in grooming behavior in rats.