Agonists acting at the serotonin-1B receptor (5-HT1BR) and 5-HT2CR have been reported to potentiate and block, respectively, the discriminative stimulus effects of cocaine. The present investigation reassessed the antagonistic effects of the mixed 5-H2C/1BR agonist m-chlorophenylpiperazine (mCPP) on the discriminative stimulus effects of cocaine in the presence or absence of selective antagonism of the 5-HT1BR or 5-HT2CR. The stimulus effects of cocaine were attenuated by mCPP at doses that reduced response rates. The selective 5-HT2CR antagonist SB 242084, but not the selective 5-HT1BR antagonist GR 127935, reversed the mCPP-evoked attenuation of the cocaine cue and the suppression of response rates. These results demonstrate that the suppressive effects of mCPP on cocaine discrimination are related to stimulation of the HT2CR.