Thirteen patients with ALL, 15 with AML and 15 healthy subjects constituted the material of the present study. IL-10 and INF-gamma were estimated in serum and PBMC of the patients and controls. All patients were early diagnosed and they were included in the study before they started the anti-leukemic therapy. Leukemic patients showed significantly higher total IL-10 and significantly lower free INF-gamma in serum and PBMC culture compared to control subjects. Significant positive correlations were detected between serum and PNMC levels of IL-10, and of INF-gamma. Significant negative correlations were detected between IL-10 and INF-gamma levels both in serum and in PBMC culture. Hb levels in leukemic patients was negatively correlated with IL-10 and positively correlated with INF-gamma levels both in serum and in PBMC culture. The possible causes of these alterations was discussed.