Hypocretins (orexins) are recently discovered neuropeptides synthesized by neurons in the lateral hypothalamus that have been implicated in a variety of behav­iors, e.g. food-seeking and feeding, reaction to stress, arousal and sleep. Disturbances in the central hypocretin neurotransmission are believed to underlie narcolepsy. It has also been postulated that hypocretins play an important role in the regulation of HPA axis, energy homeostasis, acquisition and learning of reward system-stimulating signals. In this review we discuss anatomical, neurophysiological, pharmacological and behavioral data indicating an involvement of hypocretins in reward-seeking and addiction to psychoactive drugs, including relapse to drug-seeking behavior after periods of abstinence.