The role of the Müller cell in the generation of the ERG b-wave was studied in the skate eye by examining the effects of a gliotoxic agent (alpha-aminoadipic acid; alpha-AAA) on retinal structure and function. Superfusing the eyecup for 1 h in 50 mM alpha-AAA resulted in the loss of the b-wave and extensive damage to glial cells, i.e. disruption of the cells' plasma membranes, and a marked loss of cytoplasmic substance. Of the other retinal elements, only the horizontal cells showed some signs of injury in alpha-AAA. On returning the retina to a normal Ringer solution, the widespread loss of cytoplasmic electron density persisted, but the Müller cell membranes appeared to have undergone repair, and the b-wave recovered fully its normal amplitude and waveform.