Piflutixol is a thioxanthene neuroleptic which combines a very potent dopamine antagonistic effect with a potent effect in tests for sedative properties. It was found to have a very strong antagonistic effect against stereotypies induced by dopamine agonists in mice, rats and dogs as well as against apomorphine induced vomiting in dogs. This indicates that piflutixol must be considered as one of the most potent dopamine receptor blocking agents. Piflutixol seems to be the hitherto most potent inhibitor of dopamine-stimulated adenylate cyclase. There was a linear relationship between D-1 dopamine receptor occupation by [3H]piflutixol and inhibition of dopamine sensitive adenylate cyclase. Piflutixol markedly antagonizes the effect of noradrenaline, 5-HT and to some extent histamine, whereas the affinity for muscarinic receptors was rather weak. Piflutixol has a high affinity for dopamine structures within the brain. It is a compound with a very long duration of action.