Current available measures of sexual orientation are briefly reviewed. A novel sexual orientation measure is proposed, based on experiments in operant psychology. Previous relevant studies are reviewed, and it is suggested that a deficiency is their reliance on a single response as the dependent variable. The matching law is introduced, and it is argued that this provides a potentially powerful framework within which the relative reinforcement magnitudes of sexual stimuli may be computed, using as the dependent variable the relative rates of two responses. The proposed assessment method provides a means of answering the question "What is the reinforcement magnitude of various classes of erotic stimuli for a given individual?"