ABSTRACT Vol. 245, No. 2 Printed in U.SA. In the 1 ,4-benzodiazepine (BZD) series the nature of the C(5) substituent is critical for activity. in tetrazepam this substituent is a cyciohexenyl ring, in all other clinically effective 1,4-BZD derivatives it is a phenyl ring. Schoemaker et at., 1981). Although there appears to be no significant correlation between the clinical properties of BZDs and their affinity for the pe ripheral binding site 69