The 5-HT2 receptor agonist, DOI, dose-dependently (0.16-10.0 mg/kg, s.c.) increased dialysate levels of dopamine (DA) and noradrenaline (NA), but not 5-HT, in the frontal cortex (FCX) of freely-moving rats. This action was abolished by the selective 5-HT2A antagonist, MDL100,907 (0.04), which did not, itself, modify levels of DA and NA. In contrast, the selective 5-HT2B/2C antagonist, SB206,553 (0.63), increased levels of DA and NA additively with DOI. Thus, in contrast to a tonic, inhibitory influence of 5-HT2C receptors (see Millan, M.J., Dekeyne, A., Gobert, A., 1998. Serotonin (5-HT)2C receptors tonically inhibit dopamine (DA) and noradrenaline (NAD), but not 5-HT, release in the FCX in vivo. Neuropharmacology 37, 953-955), 5-HT2A receptors exert a phasic, facilitatory influence upon FCX levels of DA and NA.