The carbonic anhydrase inhibitor methazolamide was used to test the hypothesis that carbonic anhydrase activity plays a role in the early morphogenesis of the chick eye. Methazolamide was administered topically to eyes of 4-7-day-old chick embryos in shell-free culture. Either continuous application of drug solution with a miniosmotic pump or a single daily application of drug resulted in significant reduction in embryonic eye growth relative to sham-treated controls.