The vertebrate retina contains ganglion cell types that appear to be specialized for detecting temporal changes. These cells typically respond to a static stimulus with a transient burst of action potentials only at the presentation and/or removal of the stimulus, and show a vigorous sustained discharge to dynamic inputs, such as moving stimuli. These transient and motion-senstive responses are thought to be generated by interactions in the inner retina involving amacrine cells, but the nature of these interactions is not known. One way to examine them is to remove specific cells from the circuitry and measure the effects on ganglion cell responses. Here we apply a cell-ablation technique to explore the roles of one amacrine cell subclass in the mouse retina. Ganglion cell spike trains were recorded from the isolated mouse retina using an extracellular multi-electrode array, while presenting stimuli displayed on a computer monitor. Ablation of the amacrine cell class altered the response dynamics of the ON-type ganglion cells: Their response to a step increase in uniform illumination was greatly prolonged, from ms (time above of maximal firing rate) to ms. Thus, the ablated amacrine class may normally serve to truncate a sustained excitatory input to the ON cell. To also examine spatio-temporal integration, we stimulated the retina with moving square wave gratings of 8 different orientations. In normal retinae, the response of about of all ON-type ganglion cells showed a significant dependence on the grating orientation, indicating anisotropy in their receptive field structure. In the amacrine-depleted retinae, that proportion increased about 3-fold. Thus this amacrine cell class makes strong contributions to both temporal and spatio-temporal integration by retinal ganglion cells.