Role of the spleen in tumor surgerySummary. Tumorgenesis and tumor growth are connected with the immune system. Therefore the role of the spleen respectively splen~ctomy have gained increasing influence. The existing experimental and clinical results are discussed with the help of a general review of the literature. A manipulation of the immune system by splenectomy seems possible. A common pathomechanism has not yet been found. But experimental investigations are transferrable to human beings only under special conditions.