The effect of insulin on limb regeneration of a metamorphic stage of the tadpoles of the Egyptian toad, Bufo regularis Reuss was studied by using a single dose of insulin (1 µl/individual) after amputation at the mid shank. Insulin was found to increase the regenerative power of the amputated limbs and enhance the formation of large amounts of cartilage. One case of the treated animals regenerated four toes, while four other cases restored part of the foot, which was not seen in the control group. The nature of the effect of insulin was discussed.