A thermodynamic theory is presented for the response of a tensiometer in an anisotropically loaded soil. It is argued that the tensiometer pressure is independent of the orientation of the head of the instrument, implying that a scalar moisture potential is applicable to such soils. This moisture potential is characterized in terms of other measurable properties of the soil-water system. It is suggested how to infer, for loads which produce deformations small in comparison with those due to typical changes in moisture content, the moisture potential of an anisotropically loaded system from that of the same system under isotropic loading.