Our laboratory is using both intraoral and extraoral methods of measuring the pH of dental plaque following ingestion of various test foods. Time courses for pH following sucrose ingestion are similar except the extraoral method detects the drop more rapidly than does the intraoral method. In past studies (here and elsewhere) the indwelling glass pH electrode often failed to respond properly because of moisture leakage of the intraoral connector. This problem has been eliminated by incorporating a gas tube with the wire connector. The tube emits a stream of nitrogen which keeps critical electronic junctions moisture-free and well-insulated.