1. Sperm storage tubules in the ostrich start to develop at an early stage of oviductal growth. Concurrently, membrane-bound carbonic anhydrase was found in the cells of the storage tubules. 2. In mature ostriches the utero-vaginal junction averaged 11.5+/-2.1 cm in length and primary mucosal folds were extremely long and slender. Membrane-bound carbonic anhydrase was present in the cells of the sperm storage tubules. In the non-ciliated cells of the surface epithelium both membrane-bound and cytoplasmic activity was detected. 3. The possible role of carbonic anhydrase in the stimulation/inhibition of sperm motility by altering the pH was discussed.