1. Following therapeutic x-irradiation of the spleen in patients suffering from chronic myeloid leukemia alterations in the composition of the bone marrow have been noted in a high proportion of cases. These consisted of a decrease in the number of immature myeloid cells or an increase in that of the immature erythroid cells or both.
2. Eighty minutes after local irradiation of the leukemic spleen with therapeutic doses of x-rays there was found a diminution in the number of mitoses among myeloid cells in the bone marrow.