We compared the amplitude and implicit times of the a-waves, b-waves, and oscillatory potentials of the focal macular electroretinograms of 30 eyes with aphakic cystoid macular edema and the healthy fellow eyes. Ten affected eyes were characterized by reduced amplitudes of the oscillatory potentials with normal a-wave and b-wave responses (type 1). Nine affected eyes had both reduced amplitudes of the oscillatory potentials and the b-waves (type 2). Ten affected eyes were characterized by reduced amplitude of the oscillatory potentials, the a-waves, and the b-waves (type 3). One eye could not be classified. Visual acuities were as follows: type 1, 0.55 (20/36.4); type 2, 0.31 (20/64.5); and type 3, 0.12 (20/166.7). The mean time between cataract surgery and the electroretinographic testing was significantly longer for type 2 and 3 eyes than for type 1 eyes. The differences in the electroretinographic responses between the affected eye and the normal fellow eye suggested either an increased severity or the stage of the cystoid macular edema.