A series of novel aromatic tritylamino heterocycles has been synthesized and the compounds have been tested in comparison with clotrimazole for their ability to inhibit the slow afterhyperpolarization current (sI (AHP)) in cultured rat hippocampal pyramidal neurones. Some analogues of the clotrimazole metabolite, 2-chlorophenyl-diphenyl methanol, having different chlorination substitution in the triphenyl group have also been examined. Two compounds in particular, 3-[(2-chlorophenyl)-diphenylmethylamino] pyridine (3a, UCL 1880) and 2-tritylaminothiazole (6, UCL 2027), are of special interest; they are effective blockers of the sI (AHP) (IC (50) = 1.1-1.2 microM) and are much more selective than clotrimazole since they have less effect on the high voltage-activated Ca2+ current.