The purpose of this in vitro study was to determine whether there were differences in the number and size of osteogenic and hemopoietic colonies derived from bone marrow stem cells of aged and young adult male Sprague-Dawley rats. Using a Ficoll-Paque gradient, stem cells were harvested from aged male rats 18 to 22 months old and young adult males 55 days of age. Single cell suspensions from the red marrow of the long bones were cultured 14 days in vitro and subsequent colonies were assessed by light microscopy for number and size. A computerized histomorphometric linear measuring system was utilized to assess colony area in square millimeters. The results clearly show that young animals have a statistically significant increased cellular potential for osteogenic and hemopoietic colony formation. Cultures from aged animals showed an average formation of 0.45 +/- 0.6863 osteogenic colonies while those from younger animals had an average of 3.6 +/- 2.3523 osteogenic colonies per 3 million cells plated. Hemopoietic colonies from aged animal cell cultures numbered 5.25 +/- 2.2449 while those from the young animals averaged 8.23 +/- 3.3601 per 3 million cells plated. The difference in size of the osteogenic and hemopoietic colonies between age groups was not statistically significant. The area of osteogenic colonies derived from aged animals measured 0.1244 +/- 0.0891 mm2, while those derived from the young animals averaged 0.1276 +/- 0.0518 mm2. Hemopoietic colonies from the aged cells measured 0.0759 +/- 0.0514 mm2, while hemopoietic colonies from the young animal cells measured 0.06010 +/- 0.0180 mm2. The results of this study may have implications for consideration in the cellular healing aspects of aged versus young individuals.