The electroretinogram (ERG) of the diurnal lizardAnolis carolinensiswas monitored once per hour in constant dark for periods of approximately 5 consecutive days. The amplitude of the b‐wave component of the ERG exhibited a rhythm in all eyes, while the amplitude of the a‐wave component exhibited a rhythm in only 30% of the eyes. These rhythms had a period of approximately 24 hr and their peak amplitudes occurred near projected midday. Constant light masked the b‐wave rhythm, but only produced a phase delay in the a‐wave rhythm. ERGs were also monitored from the nocturnal lizardGecko geckoin constant dark. The amplitude of the b‐wave exhibited a rhythm that had a period of approximately 23 hr, and its peak amplitude occurred near projected sunset. In contrast to the b‐wave, there was no evidence for a rhythm in the a‐wave.