The appropriate use of hypnotics requires an understanding of the nature of the patient's insomnia and lifestyle. In the context of occupational medicine, the potential effects of these drugs on job skills and the persistence of such effects are also important considerations. This report reviews the factors that must be considered in the investigation of impaired performance due to hypnotics and the pharmacokinetic properties that determine the persistence of action of these drugs. Sleep disturbance associated with transmeridian flights (jet lag) is used to illustrate the place of hypnotics in the management of a transient form of insomnia.