The pineal gland plays an important role in the production of melatonin and in the synchronization of the reproduction process in seasonal breeding animals. Changes in the duration of day length are the most important stimulatory factors. In humans the pineal gland may not only have a physiological role in the seasonality of maturation, but also concerning the simultaneously observable changes of serum hormone and serum melatonin levels as well as in regard of changes in hair colour in prepuberal children. Therefore the pineal gland seems to play an important physiological role in the timing of human maturation.