The synthesis of 10-piperazinyl-4H-thieno[3,2-b][1,5]benzodiazepines is described. The activity of these compounds has been assessed on the basis of their ability to produce hypothermia in mice and block a conditioned avoidance response (CAR) and produce catalepsy in rats, and the results are compared with various classical and nonclassical neuroleptic drugs. A number of compounds (6, 17, 21, and 22) demonstrate potency greater than clozapine and also show low degree of catalepsy. It is believed that this profile of activity, unlike standard neuroleptics, is associated with the relative lack of extrapyramidal side effects in the clinic. The corresponding 9-piperazinyl-4H-thieno[1,4]benzodiazepines (12 and 35, limited analogues prepared in the respective series, were inactive.