A preliminary experiment showed that a 2.5 mg/kg dose of the 5-HT agonist 1-(3-chlorophenyl)piperazine di hydrochloride (mCPP) produced a greater reduction of food intake in female rats when weight-matched rats of both sexes were compared following 24 h food deprivation. A second experiment showed that this dose of mCPP led to higher drug concentrations in female than in male brain tissue. In two meal pattern studies non-drugged females took a shorter first meal, but ate more rapidly during that meal, than males; these differences were also seen in records of ad libitum feeding. mCPP produced an anorectic effect that lasted for < 1 h with rebound feeding becoming apparent within 1-2 h. The drug increased latency to feed, reduced the size of the first meal and feeding rate during that meal and had effects that were most marked in older rats and in female rats. In addition, effects of mCPP on water intake were as profound as those on food intake. These effects are discussed in relation to sex differences in feeding and the behavioural specificity of mCPP.