The function of megakaryocytes in femur bone marrow of dog after left side lumbar sympathectomy or left side parasympathectomy, sectioning the posterior roots of fifth, sixth and seventh lumbar spinal cord as well as the first sacral segment, was observed by means of clinical bone marrow tissue culture. And also observed the change of platelet counts in nutrient vessel of tibia after these operations, comparing with those on the another right side as control. The results are as follows. 1) In the cases of sympathectomy, megakaryocyte functions (number of megakaryocytes in growth zone, percentages of moving type of megakaryocyte and tentacle formation type for platelet formation) on bone marrow tissue culture was accelerated. And the platelet counts in nutrient vessel of tibia was increased on the sympatheticomized side. The maxima of these changes were showed on around 10th day after the operation, then these changes had been disapeared until 60th day. 2) Megakaryocyte function on the parasympatheticomized cases was diminished. And also the platelet counts in nutrient vessel of tibia was decreased on the parasympatheticomized side. The maxima of these changes were on around 10th day. But the change of number of megakaryocytes in growth zone was maximum on 5th day after the operation. These results should be presumed that sympathetic denervation introduce increase of blood flow in the bone marrow and parasympathetic denervation introduce decrease of blood flow in the bone marrow, then secondarily lead up to increase or decrease the function of megakaryocytes. Futhermore, it may be thought that parasympatics influences some direct effect for the function of megakaryocytes in bone marrow.