Previous attempts to condition a 1-celled organism, paramecium, by either classical or instrumental procedures, have yielded equivocal results. The present experiments were designed to determine whether the use of positive reinforcement provided by DC electrical stimulation at the cathode, which had previously been shown to be attractive to paramecia, could be used to train these organisms in a discrimination learning task. The results indicate that such learning did take place. (Contains 3 figures.)