Iontophoretically applied dopamine reversibly altered both the spontaneous firing rates and the light evoked responses of retinal ganglion cells in the intact eye of the cat. The effects of dopamine were the same for all cell classes encountered: on brisk-transient, off brisk-transient, on brisk-sustained, off brisk-sustained, sluggish and non-concentrically organized cells. Dopamine reduced the spontaneous firing rates of all cells. In response to light stimulation, the inhibitory response phase (light off in on ganglion cells, light on in off ganglion cells) was also reduced by dopamine. However, the excitatory response phase (light on in on ganglion cells, light off in off ganglion cells) was only consistently reduced for optimal spot stimulation: for wholefield or annular stimulation the excitatory response phase was reduced in 76% of cells, whereas for the remaining cells it was unchanged or even increased. The net effect of these alterations was to cause a shift in the centre surround balance of the cell output in favour of the centre for 82% of concentrically organized cells. These results are discussed in the context of present anatomical knowledge.