In the retina of vertebrates, carbonic anhydrase (CA) is present in the cells of the pigmented epithelial layer and in Muller cells. Its activity has been demonstrated to increase during development, corresponding to the maturity of the tissue. We have studied CA activity, either during embryonic development or after hatching, in the retina of 3 species of birds, having precocial or atricial broods. The research has been carried out, by histochemical and biochemical methods, in pigeon as an example of atricial brood, and in fowl and quail, that represent examples of precocial broods. Our results confirmed that CA activity may be taken as a marker of retina maturity, or, more precisely, of Muller cells maturity, for any species of vertebrates, depending solely on maturity of the offspring at birth time.