We assessed mRNA for chosen pro- and anti-inflammatory cytokines in T-lymphocytes of peripheral blood in paediatric patients with leukemias and lymphomas. Levels of four different cytokine mRNAs (IFN-gamma, IL-10, IL-4, TGF-beta) were determined by the real-time PCR technique. In the whole examined group, at the time of diagnosis, we noted lower amounts of mRNA for TGF-beta1, comparing to respective values in the control patients. In the ALL group, we observed the following: 1) at the time of diagnosis: lower amounts of mRNA for IL-4 and for TGF-beta1, comparing to respective values in the control group; 2) lower amounts of mRNA for IL-10 after remission induction, comparing to the time of diagnosis. In our opinion, "immunedysregulation" in lymphoproliferative diseases in children is not caused by IFN-gamma deficiency. The deficit of anti-inflammatory cytokines, i.e., IL-4, TGF-beta, with higher amounts of IL-10, suggests their role in cancer development.