Using a culture system that facilitates osteogenic differentiation of bone marrow-derived human mesenchymal stem cells, we analyzed gene-expression profiles during the mineralization process by means of a cDNA microarray system consisting of 23,040 genes. We compared expression profiles of the cells at days 3, 15, and 27 of incubation in media containing either a combination of 0.1 muM dexamethasone, 0.05 mM ascorbic acid-2-phosphate, and 10 mM beta-glycerophosphate, dexamethasone only, ascorbic acid-2-phosphate plus (-beta)glycerophosphate, or medium without any of these osteogenic supplements. Histochemical analysis revealed osteogenic differentiation of cells incubate in the presence of all three agents, but not in the other cultures. Comparison of the expression profiles disclosed transcriptional stimulation of 55 genes and repression of 82 genes among more than 20,000 examined. A set of differentially expressed genes we report here should contribute to a better understanding of the process of mineralization in the matrix surrounding human mesenchymal stem cells. (C) 2002 Elsevier Science.