Analysis in the frequency domain divided the pattern-evoked retinal response (PERR) of the cat into two analog components. A mild respiratory acidosis was produced by raising the end-tidal CO2 from 4-6% to 12-14%. The onset of the acidosis (without hypoxia) was highly correlated with marked decreases in the low-frequency PERR component and in the b-wave of the flash-elicited ERG. The high-frequency PERR component was unchanged relative to the labile low-frequency component (p less than 0.01). The literature has established a firm link between local pH and Müller cell function. These data tend to confirm the hypothesis that the cat's PERR to some grating stimuli of less than 100% contrast may contain separable components of different cellular origin(s).