On the basis of the anxiolytic property of ripazepam, 1-ethyl-4,6-dihydro-3- methyl-8-phenylpyrazolo[4,3-e][1,4]diazepin-5(1H)-one (1), a series of isomeric 5-(phenyl-substituted)pyrazolo[4,3-e][1,4] diazepin-8-ones 3a-f were prepared and tested for their ability to bind to the benzodiazepine receptor. All compounds 3a-f display affinities for the benzodiazepine receptor in the microM range of concentration; in particular 5-phenyl-3-methyl-6,7-dihydropyrazolo[4,3-e][1,4] diazepin-8(7H)-one (3a) is 2 orders of magnitude less potent in inhibiting [3H]flunitrazepam binding than diazepam and displays an affinity for the benzodiazepine receptor practically comparable to that of its structural isomer, ripazepam, and to that of chloriazepoxide.