At present, no clinical electrophysiologic test defines dysfunction of the retinal pigment epithelium. We studied four electrophysiologic responses of the retinal pigment epithelium to compare results from three normal subjects with those from three patients with a diffuse retinal pigment epithelial disorder, extramacular drusen. We recorded the fast oscillation, hyperosmolarity response, acetazolamide response, and light peak by means of a clinical protocol in which these could be elicited consecutively. We found no significant differences between the normal subjects and patients with drusen for any of the four responses. These results suggest that retinal pigment epithelial electrophysiologic function is well maintained despite the widespread physical abnormalities of the retinal pigment epithelium in extramacular drusen. This combined test was well tolerated and may prove useful in characterizing other diseases involving the retinal pigment epithelium.