Retinal bipolar cells can be divided into ON and OFF types, based upon the polarity of their response to light. Bipolar activity is further shaped by inhibitory feedback, characterized here by the events that occur immediately following the onset of a light step: 1) In most OFF bipolar cells, excitatory current decreased while inhibitory current increased. These currents reinforced each other, enhancing the light response. 2) In about half of the ON cone bipolar cells, the excitatory current increased while inhibitory current decreased, also reinforcing the light response. Both of these reinforcing interactions were mediated by glycinergic inhibition. 3) In the remaining ON cone bipolar cells, excitation and inhibition both increased, but inhibition was delayed, so that these cells responded transiently. 4) Finally, in rod bipolar cells, excitation and inhibition both increased, so that inhibition suppressed excitation, reducing the light response at all time scales. The suppressive inhibition seen in ON cone and rod bipolar cells was mediated by GABA. Thus, morphologically diverse bipolar cells receive only four main types of inhibitory input, and the majority of inputs, conventionally described as inhibitory, actually serve to enhance excitation.