Place conditioning is one of the most popular behavioral methods for assessing the rewarding properties of various substances. Many substances that are rewarding also influence motor activity. This report describes a computerized system designed to simultaneously monitor both place conditioning and locomotor activity. The system consists of 4 independent conditioning boxes, each equipped with 6 pairs of photosensors connected to an Experiment Controller, an electronic board containing a microprocessor, a programable timer, and 16 K of RAM used to store both instructions and data. The effects of the stimulant (+)-amphetamine were assessed using this system and found to produce a place preference comparable to that obtained from a previously utilized mechanical timer system. The computerized system also demonstrated that amphetamine increased unconditioned activity. There are a number of advantages and broader applications of the new methodology.