The behavioural specificity of the eating elicited by the serotonergic agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) was investigated. In non-deprived rats 8-OH-DPAT (60-240 micrograms/kg) increased the consumption of solid food pellets. The consumption of an 18% glucose solution was unaffected by 60 micrograms/kg 8-OH-DPAT, and markedly reduced by 120 micrograms/kg 8-OH-DPAT. When rats were pre-fed glucose, to reduce glucose intake under control conditions, 60 micrograms/kg 8-OH-DPAT significantly decreased subsequent glucose consumption. The failure of 8-OH-DPAT to induce a hyperphagic response to glucose suggests that this compound does not elicit eating by an action upon feeding motivation. Observational analyses showed that 8-OH-DPAT-treated rats exhibited several oro-facial motor responses, including gnawing, which were attenuated by pretreatment with haloperidol. It is likely, therefore, that the increase in solid food intake elicited by 8-OH-DPAT is incidental to drug-induced gnawing. Possible mechanisms of this action are discussed.