In 24 patients with Hodgkin's disease the activity of acid phosphatase was determined in granulocytes. Its level was only half that in the control group. The causes of this low activity of this enzyme may be increased number of cells without it, exocytosis, and possible influence of substances secreted by the neoplasm. It is suggested that the determination of this activity may be indirectly useful for verification of the efficacy of the antibacterial mechanisms, and also of antitumour resistance of the host.