Dermal fibroblasts from three healthy controls and three patients with PXE were cultured on 24-well plates in DMEM medium containing 10% fetal bovine serum. At day 0, some cultures were supplemented with 4 mM Pi with or without 3 μM minocycline. At day 10, the degree of calcification was assessed either (a) by phase contrast light microscopy or (b) by chemical assay of calcium deposition in the cell layer normalized by the protein content. Data were represented as mean ± SD; *P < 0.05, **P < 0.01. n = 3 replicate cultures for each fibroblast. Ctr, control; Mino, minocycline; Pi, inorganic phosphate; Bar = 400 μm.