['This study was to investigate the variables in bone marrow harvesting procedure and individual donor factors which can potentially affect the yield of mesenchymal stromal cells (MSC).', 'WE DETERMINED THE YIELD OF MSC FROM BONE MARROW UNDER DIFFERENT CLINICAL CONDITIONS BY COMPARING THE MSC COLONY NUMBERS FROM: (1) donors of different ages; (2) healthy donors and patients with leukemia; (3) bone marrow aspirated at different time points during marrow harvesting; (4) bone marrow harvested by different needles.', 'During the process of harvesting, the number of MSC significantly decreased with increase number of aspiration, from 675/ml at the initial decreased to 60/ml after 100 ml bone marrow aspirated, and 50/ml after 200 ml bone marrow aspirated. The number of MSC retrieved from leukemia patients (99/ml bone marrow) was significantly lower than that of healthy donors (708/ml bone marrow). However, there was no significant difference in growth rate. There was no significant age-related difference of MSC yielded from donors <55 years. And there was no significant difference in MSC number between the samples from single end-holed needle and those from multiple-side-hole needle.'] Do factors affecting mesenchymal stromal cells yield from bone marrow aspiration?