The anterior semicircular canals of bull frogs were isolated, and the cupula was removed from the crista and the sensory cilia on the crista were depressed toward the canal side by a glass micropipette. Seven points on the crista were selected for stimulation. Decremental time constants of the anterior ampullary nerve action potentials were measured. The longer time constants were measured at the lateral points of stimulation which progressively shortened towards the central point. The overall values of the time constant were significantly shorter than those of the posterior semicircular canal. This indicates that the anterior semicircular canal has a larger number of phasic receptors than the posterior canal.