A reliable method has been developed for the staining of mammalian retinal neurons in the isolated eyecup. Small injections of horseradish peroxidase are made at a number of places on the retinal surface while the hemisected eyecup preparation floats in Eagle's medium. After 30 min, the retinas are removed, fixed, and reacted with diaminobenzidine. Golgi-like staining of fine dendrites, spines and axons of ganglion cells is achieved. The method also stains amacrine, horizontal and bipolar cells.