The author reflects on the history of the discovery of the relationship of external influences, cyclicity in nature, and the internal biological clock in man. He presents his own series of patients suffering seasonal affective disorder fulfilling the criteria of the major depression, as well as experience with its photothera- peutic treatment. From the economic point of view, phototherapy seems to be an appropriate method supp- lementing medication

        Key words: phototherapy - depressio - seasonal affective disorder