The authors studied histochemically the enzymatic sites of retinal cholinesterase activity in the albino rabbit during different early postnatal periods. The retinae of young rabbits weighing approximately 60 gm. whose palpebrae were still fused and unable to function for sight, and of rabbits weighing approximately 300 gm. which were able to see, were obtained immediately after killing the animals by the intravenous injection of air or by decapitation and fixed in formalin-sucrose ammonia fixative, as recommended by Pearson (1963), for about 24 hours and incubated in the substrate containing acetylthiocholine, iodide, as presented by Gerebtzoff (1953), at 37degrees C. for 2 to 3 hours. After the treatment of the retinae, as devised by Koelle and Friedenwald (1950), the retinae were sectioned at 5 micra and mounted both without counterstaining and after counterstaining with hematoxylin alone.