5-HT receptor positively coupled to adenylyl cyclase in striatal neurones in culture does not correspond to the 5-HT4 receptor. 5-HT induces an increase in cAMP level with an EC50 of 125 nM. 5-HT agonists displayed the following rank order of potencies 5-HT > LSD > 5-MeOT > 5-CT. 8-OH-DPAT, RU 24969 and cisapride were inactive. The most efficacious antagonists were methiothepin and tricyclic antipsychotic drugs (clozapine, amitriptyline and nortryptyline). The pharmacological profile defined by both functional studies (cAMP level) and binding experiments ([125I]-LSD binding), and its localization in striatal neurones are in favour of the presence of the recently cloned 5-HT6 receptor in these cells.