The current data concerning the efficacy of exogenous melatonin treatment, especially with respect to night-shift workers, are presented. Therapy of sleep disorders experienced by night-shift workers is not always successful. To assess the results of melatonin therapy in shift workers, it is essential to perform extensive analyses of numerous physiological functions that may be affected by this work system as well as of possible late health effects in this group of workers. It is also necessary to establish indications and conditions for this kind of therapy. We may suspect that both night-shift work tolerance and efficacy of melatonin therapy are different in individual workers, and thus the choice of therapy should be based on a thorough examination of each worker's psycho-somatic conditions.