Abstract
Lethally irradiated mice were injected with 1×105 normal bone marrow cells taken from mice of the same strain. They were divided into two groups: One was given chloramphenicol (CAP) or thiamphenicol (TAP) in an early stage after marrow transfusion and the other in a later stage. In both groups, more prominently in the former group, some ultrastructural changes were recognized in mitochondria of the early erythroblasts. Mitochondria increased in number and became swollen with electron lucent matrix and paucity of cristae. Condensed mitochondria described in earlier reports were never observed. Intermediate or late erythroblasts seen only in the latter group did not show such alterations. Mitochondrial changes in the early erythroblasts were considered to reflect the dose-related toxic effects of CAP and TAP, and it is assumed that these drugs affect the development of erythroblasts in a very early stage.
