The expression of resistance-related proteins P-170, GST-pi, Topo II, TS and MT was investigated. Patients who developed a relapse expressed more than two resistance mechanisms significantly more often than patients who remained remission (p = 0.005). The higher the number of resistance-related proteins in childhood AML the poorer the prognosis of the patients. The gene discussed is TYMS; the disease is acute myeloid leukemia.