Sedative hypnotics belong to several chemical classes and thus have heterogeneous pharmacodynamic properties. Among various ways of approaches, conventional pharmacology using animal models allows one to define a common pharmacological profile. It still remains the best predictive tool of hypnotic efficacy in man. The study of discriminative properties is a useful extension of these conventional models. Electrophysiological and biochemical studies allow primarily to approach the problems of the sites and mechanisms of action, but only begin at the moment to lead to practical applications.