SSRI acts by blocking the serotonin transporter (5-HT), increasing the availability of serotonin at the synaptic cleft averting its reuptake. The increment of serotonin activates 5-HT1A presynaptic autoreceptors, resulting in a modulation in the release of serotonin by the presynaptic neuron. It is proposed that 5-HT1A receptor antagonism could accelerate the clinical effect of antidepressants by preventing this negative feedback.Preclinical data obtained with selective 5-HT1A antagonists, such as pindolol, and with mice lacking 5-HT1a receptors supports this hypothesis. Results on partial antagonists (pindolol) are conclusive in accelerating SSRI. It is reasonable to call into question whether a total antagonism of 5-HT1a receptors could imply a more rapid antidepressant response. To test this hypothesis we conducted a double blind, randomised, controlled trial with DU 123550 added to fluoxetine 20 mg/day