In Catfish, the kidney is the hemopoietic organ. On heart imprints of Catfishes, there were observed cells of the hemopoietic series. In this work it was studied how much the heart can intervene in the erythropoietic process. In normal animals the heart intervenes as a erythropoietic organ in the spring when the hemopoietic activity is more intense. In partially nephrectomized animals the heart has an erythropoietic activity also when, after nephrectomy, the hematic equilibrium has returned to normal. Cells at the same stage of development were observed on the heart and on the kidney of partially nephrectomized animals. In animals treated with acetylphenylhydrazine (hemolitic agent), the heart intervenes in the erythropoiesis also when hematic equilibrium is lightly altered. The lymphoid hemoblasts are also shown to be precursores of red cells.