A laboratory method for obtaining tensiometer measurements on surfaces of porous rock and soil is presented. The construction and performance of two versions of the surface tensiometer, developed for determining near-zero values of matric potential on rock surfaces, are described. Laboratory surface tensiometer measurements were made on a natural fracture surface of a Bishop Tuff block equilibrated with a water table boundary set at elevations ranging from -51 to +25 mm relative to the tensiometers. All equilibrium readings were within 10 Pa of ideal values, and most were within 5 Pa. Response times associated with this instrument-rock system were in qualitative agreement with the matric potential-dependent hydraulic properties of the rock block.¿ 1997 American Geophysical Union