The binding kinetics, pharmacological properties and regional ontogeny of L-[3H]glutamic acid Na+-independent and [3H]kainic acid binding sites were studied in preparations of chick brain. One binding component was found for L-[3H]glutamic acid with a Kd value of 176 x 10(9) M. For [3H]kainic acid two binding components were found in the hemispheres, optic lobes and brain stem, one with high affinity and a Kd value of 12.5 x 10(9) M and one with low affinity and a Kd value of 260 x 10(9) M. In cerebellum only one binding site was detected for [3H]kainic acid with a Kd value of 144 x 10(9) M. The ontogeny of L-[3H]glutamic acid and [3H]kainic acid binding sites was studied using membrane preparations (48,000 g pellet) of hemispheres, optic lobes, brain stem and cerebellum. Binding of L-[3H]glutamic acid was already significant in all brain regions by embryonic day 11 but major increases in total receptor number per brain region or per mg of protein were apparent by embryonic day 19 and especially after hatching. Cerebral hemispheres, optic lobes and brain stem showed few [3H]kainic acid binding sites by day 13 in ovo. An increase follows which, in hemispheres and optic lobes, continues at the same rate during the first two weeks after hatching. In cerebellum, by contrast, the kainic acid binding site is almost undetectable until embryonic day 15. The appearance of these binding sites in cerebellum takes place during the restricted period between days 15 in ovo and 5 post-hatching. This pattern of development of [3H]kainic acid binding sites almost parallels the developmental patterns of the molecular layer of chick cerebellum and it is consistent with the results of our autoradiographic study showing that the great majority of kainic acid binding sites are localized in the molecular layer.