Studies of the mechanisms of osteoporosis have not yet determined whether these conditions result from increased osteoclast activity or decreased osteoblast activity, or perhaps both. Osteoporosis is related to aging and to postmenopausal status. The function and the mitotic capacity of cultured human osteoblast-like cells were investigated in this study. The age at which these cells lose the ability to divide showed a strong negative correlation with donor age (r = .815, p < .01). There was also significant correlation of maximum cell saturation density with donor age (r = .698, p < .01). Alkaline phosphatase (ALP) activity and mineralization ability, typical functions of osteoblasts, continue undiminished up to the point at which mitotic capacity ceases. When cells were treated with 1α,25-dihydroxy vitamin d3 in the presence of 2 mM α-glycerophosphate, ALP activity and mineralization ability showed an increase, rather than a decrease, with advancing donor age. However, these functions showed no correlation with in vitro cell aging. We propose that human osteoblast-like cells from elderly subjects do not lose their functions of mineralization and ALP formation, and that loss of these functions with cell aging does not correlate with advancing age.