If the reference electrode of a pH meter is permitted to contact the paper suspended in an aqueous medium, the pH observed is lower than that observed with no contact. The effect has been observed with papers of widely different pH, and varies in magnitude with the proximity of contact and with different papers. The problem can be avoided by taking measurements on decanted equilibrium solutions instead of suspensions of paper. The cause of this effect may be analogous to the suspension effect in colloidal systems. -- CAL