Low amplitude (<10 μV) cone electroretinograms, elicited with 30-Hz white flicker from 59 patients with retinitis pigmentosa, were computer-averaged alone or in combination with a narrow-band electronic filter that increases the signal to noise ratio, thereby making it possible to evaluate the electroretinograms of most patients with retinitis pigmentosa. Narrow-band filtering reduced the amplitude of computer-averaged responses by an average of 7%, but the change in amplitude was independent of the size of the unband-passed response. Narrow-band filtering also allowed measurement of 30-Hz cone responses in patients followed up over an 11- to 15-year period and quantitation of responses of less than 1 μV, which were not detectable with computer averaging alone.