Murine fibroblast L929 cells were cultured for 605 ks on 316L stainless steel and titanium specimens and a cell adhesive layer was formed. Tip of a tungsten microelectrode was placed at the intracell layer and a few millimeters above the cell layer, and pH values of the intra- and extracell layer were measured, respectively. The pH values of the intracell layer on metallic specimens were apparently lower than that of the extracell layer. Therefore, the pH on metallic materials decreases with cells, that is probably caused by corrosion reaction as well as chemicals generated by cells. (C) 2004 The Electrochemical Society.