Abstract: The serotoninergic system is known to modulate mood, emotion, sleep and appetite and thus is implicated in the control of numerous behavioural and physiological functions. Decreased serotoninergic neurotransmission has been proposed to have an important role in the aetiology. Serotonin (5-HT) and the 5-HT receptors are proposed to play a key role in the neurobiology of affective disorders. The present study examined the pharmacological effects of a new series of indole derivatives. In order to obtain compounds acting as agonists and/or antagonists on the serotonin (5-HT) receptors we decided to study new compounds able to reduce the 5-HT contractions on guinea-pig ileum significantly.