Studies with human and animal culture systems indicate that a sub-population of bone marrow stromal cells has the potential to differentiate into osteoblasts. There are conflicting reports on the effects of age on human marrow-derived osteogenic cells. In this study, we used a three dimensional (3D) culture system and quantitative RT-PCR methods to test the hypothesis that the osteogenic potential of human bone marrow stromal cells decreases with age. Marrow was obtained from 39 men aged 37 to 86 years, during the course of total hip arthroplasty. Low-density mononuclear cells were seeded onto 3D collagen sponges and cultured for 3 weeks. Histological sections of sponges were stained for alkaline phosphatase activity and were scored as positive or negative. In the group ≤ 50 years, 7 of 11 samples (63%) were positive, whereas only 5 of 19 (26%) of the samples in the group ≥ 60 years were positive (p = 0.0504). As revealed by RT-PCR, there was no expression of alkaline phosphatase or collagen type I mRNA before culture, however there were strong signals after 3 weeks, an indication of osteoblast differentiation in vitro. We performed a quantitative, competitive RT-PCR assay with 8 samples (age range 38–80) and showed that the group ≤ 50 years had 3-fold more mRNA for alkaline phosphatase than the group ≥ 60 years (p = 0.021). There was a significant decrease with age (r = − 0.78, p = 0.028). These molecular and histoenzymatic data indicate that the osteogenic potential of human bone marrow cells decreases with age. J. Cell. Biochem. 82: 583–590, 2001. © 2001 Wiley-Liss, Inc.