of magnitude higher affinity for the receptors than diazepam. Planarity was one of the structural requirements for binding to benzodiazepinereceptors. The activities of agonists and inverseagonists were assessed on the basis of inhibition or facilitation of the pentylenetetrazole-induced convulsions, respectively. Thien-3-yl compounds exhibited inverseagonist activity whereas thien-2-yl analogues