The synthesis of new tetracyclic 1,4-diazepine derivatives is described. In these compounds, an additional five-membered heterocycle is fused on the known tricyclic ring systems imidazo[1,5-a][1,4]benzodiazepine and imidazo[1,5-a]thieno[3,2-f][1,4]diazepine. Many of these new compounds display a very high affinity to the benzodiazepine receptor in mammals.