Bovine muscle carbonic anhydrase III was purified to homogeneity by the strategy of rapid ion-exchange chromatography. The ionic exchanger used was CM-cellulose, and this is the first application of this technique on a cation exchanger. Nitrogen gas was used to pressurize the chromatographic column to accelerate the elution. The results show that proteins with high isoelectric points can also be purified in this way. The procedure is very time-saving compared with conventional chromatography, reducing the elution time five-to ten-fold. The proteins are in addition protected against oxidation by air.