[en] Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by ³⁵Cl NQR method in order to find the correlation between electronic structure and biological activity. The ³⁵Cl NQR resonance frequencies (ν _Q) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period (t _0.5), affinity to benzodiazepine receptor (IC₅₀) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of ³⁵Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software