The aim of this work was to define the possible occurrence of hematological changes during the course of a chronic ingestion of 137Cs. A mouse model was used, with ingestion through drinking water with a cesium concentration of 20 kBq l-1. Ingestion started in parent animals before mating, and 137Cs intake and its effect on the hematopoietic system was studied in offspring at various ages between birth and 20 weeks. 137Cs content was measured in various organs, indicating that 137Cs was distributed throughout the organism including lymphohematopoietic organs, i.e., femurs, spleen and thymus. However, we did not observe any effect on the hematopoietic system, whatever the parameter used. In fact, blood cell counts, mononuclear cell counts and progenitor frequency in bone marrow and spleen, and Flt3-ligand, Erythropoietin, G-CSF and SDF-1 concentration in plasma remained unchanged when compared to control animals. Moreover, phenotypic analysis did not show any change in the proportions of bone marrow cell populations. These results indicate that, although 137Cs was found in all organs implicated in the hematopoietic system, this did not induce any changes in bone marrow function.