The studies have been performed in 27 ALL patients, aged 4 to 21 years, during their first remission induced by the Memphis Center therapeutic schedule (New Eng. J. Med., 1974, 5, 1230). The onset of therapy with zinc took place immediately after cessation of remission supporting treatment (Vincristine, Prednison, intrathecally administered Methotrexate). During the seven days period of investigation all the patients studied were simultaneously treated with 6-Mercaptopurin. The patients were divided into two groups. The first group (15 subjects) received 0.02 mg Zn per kg of body weight (in the form of zinc sulphate prepared by Kutno Pharmaceutical Establishment POLFA). The second group (12 subjects) received placebo. The zinc administration resulted in statistically significant (p less than 0.05) increase in the TEa5' percentage and the increase of both percentage and absolute number of TEt60', whereas the serum total gamma globulins, as well as IgG, IgA and IgM levels exhibited no alterations. The examined indices of both humoral and cellular immunity did not change in the control group. The zinc therapy was not accompanied by side effects, except the slight decrease in the granulocyte count. The final opinion concerning the clinical use of zinc as cellular immunity stimulatory agent in the ALL therapy deserves further studies.