Plasma Zinc (Zn), copper (Cu), Cu/Zn ratio, and Thymidine Kinase (TK) were measured in 15 patients with leukemia and lymphoma against 10 controls. Seven patients were studied at initial diagnosis, whereas 8 were studied during remission. Although a good correlation (r = 0.4) between TK and Zn levels was found in controls, no significant correlation was shown between Zn, Cu, Cu/Zn ratio, and TK in the patients. Further studies are required with a larger number of patients. J. Trace Elem. Exp. Med. 14:5–9, 2001. © 2001 Wiley‐Liss, Inc.