Iron induces mdm2 gene expression by normal human synovial cells. Following incubation in the presence or absence of ferric citrate (1 mM) or the same concentration of sodium citrate for 9 days, RNA was isolated from normal human synovial cells and probed using a microarray (GEArray no. 9 905 020; SuperArray. The left membrane demonstrates the pattern of gene expression in cells cultured with ferric citrate, and the right membrane shows the pattern following exposure to sodium citrate. This experiment was repeated with similar results and consistent induction of these genes was observed.