In the present work we report a Fourier Transform Infrared (FT-IR) analysis performed on rat encephalon samples in the CH-OH vibrational stretching region (2400-3800) cm(-1), in order to reveal the presence of a very diffuse commercial benzodiazepine: VALIUM. The comparison between the spectral features of normal brain and the ones of samples with administrated substance has unambiguously showed that the CH stretching region seems not to suffer from any change for the pharmacological treatment, instead the OH band is strongly modified probably due to the presence of a new spectral contribution characteristic of diazepam molecule.