1. One binding component with a Kd value of 200 x 10(-9) M and half-life of the ligand binding component of 30 min was found. 2. Chloride ions produced a significant increase of L-[3H]aspartate and L-[3H]glutamate binding. 3. L-Glutamate, L-ibotenate, L-quisqualate, and DL-homocysteic acid were potent inhibitors of L-[3H]aspartate binding. 4. In all brain regions major increases of binding were observed during the third week of the in ovo period of life.