The responses of depolarizing bipolar cells to glutamate were investigated in the superfused isolated goldfish retina. In intracellular recordings with potassium-filled microelectrodes, glutamate hyperpolarized cells but did not alter the net input conductance. In recordings with cesium-filled microelectrodes, the glutamate-evoked hyperpolarization was associated with a net conductance decrease. In the presence of internal cesium, glutamate action had the same reversal potential as the actions of the glutamate analog 2-amino-4-phosphonobutyrate (APB) and the rod transmitter, suggesting that all three of these substances act at the same class of receptor. We propose that glutamate acts both at the APB-sensitive receptor that mediates rod inputs and at another receptor type that produces a conductance increase, is blocked by cesium, and may mimic the action of the cone transmitter.