The potential difference (PD), short circuit current (SCC) and resistance (R) of rabbit retina-retinal pigment epithelium-choroid-sclera preparations were measured in a modified Ussing chamber. The rabbits were kept in 14 hour light/10 hour dark cycle conditions for 14 days: tissues were taken for measurement at 1.5, 6, 13, 20 and 23 hours after the start of the fifteenth light period. Significant variations in PD and SCC were observed 6 hours into the light cycle while the resistance remained constant during the test period. When in a second experiment the fifteenth light period was replaced by darkness, the highest PD and SCC values recorded occurred 12 hours after the time when the light period should have started in the normal light/dark cycle. In a third experiment the fifteenth light period was replaced by darkness and the retina was removed. There were variations in the PD and SCC as in the second experiment but the SCC peak was reduced in amplitude. From these preliminary studies it is suggested that these variations may be circadian in origin and may be related to variations in retinal function. © 1991 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.