AbstractMuscarinic binding sites were measured using the radioligand [3H]quinuclidinyl benzilate (QNB) in the retina and tectum of 11‐day‐old chick embryos, after intracerebral administration of 0.02 μg of corticosterone at 8 days of incubation. This age was chosen because the hormone preferentially accumulates in retinas at 8 days of development. Hormone treatment significantly affected the affinity of3H‐QNB‐binding sites in retinas and slightly affected the affinity in treated tecta, whereas the number of binding sites remained unchanged. The specific binding was determined with either atropine or unlabeled QNB. Scatchard plot analysis of specific3H‐QNB binding revealed the presence of nonsaturable binding at high 3H‐QNB concentrations (6‐11 nM) in the treated retinas, but not in controls. It can be concluded from these data that the hormone has a primary effect on retinal cells during early growth in the chick embryo. The possibility that the hormone delays maturation of specific populations of retinal cells is considered in