ZINC is a trace metal of physiological importance which is widely distributed in many enzyme systems. Changes in the activity of certain enzymes have been reported in normal and tumour tissues of tumour-bearing animals1 and of man2, and in the serum of patients with neoplastic diseases3–7. Since the activity of some enzymes depends on the presence of specific trace metals, cellular derangement resulting in neoplasia may be linked with changes in trace metal concentration. Differences in zinc concentration in normal and tumour tissue in experimental animals and in man have been previously reported8–15.