Hemopoiesis in bone marrow of monkeys after spaceflight.

In six rhesus monkeys flown on Bion 9, 10, and 11, peripheral blood and bone marrow were examined. After the Bion 11 flight, two ground control experiments were performed at R+17 and R+45. The real flight caused changes that were not seen after the control experiments: decreases in hemoglobin, hematocrit, and reticulocytes. During the readaptation period, those parameters returned to normal due to stimulated erythropoiesis and myelopoiesis.