We present a method for maintaining the isolated retina-eyecup of the rabbit in a manner which permits the introduction of pharmacological agents at a controlled concentration. As judged by physiological criteria, the retina is well maintained under these conditions. The stability of the preparation is excellent; intracellular or extracellular recordings from single cells can be maintained through multiple solution changes. By using Co2+ to block synaptic transmission, we can distinguish direct from transsynaptic effects. Use of this preparation should facilitate the investigation of neurotransmission in the mammalian retina.