1. Two forms of carbonic anhydrase, having isoelectric points of 6.1 and 5.8, were purified from erythrocytes of the toad, Bufo marinus, and the presence of a third form, pI = 5.4, was demonstrated. 2. Each of the two purified isozymes catalyzed the hydration of CO2 and the hydrolysis of nitrophenyl acetate esters at rates characteristic of Type C (or high-activity) forms of carbonic anhydrase. 3. Both forms of the erythrocyte enzyme have similar molecular weights (approx 29,000), amino acid composition, sensitivity to acetazolamide, and kinetic properties. 4. The epithelium of the toad's urinary bladder also was found to contain significant amounts of carbonic anhydrase, which appears by isoelectric focusing to be indistinguishable from the enzyme isolated from the erythrocyte.