When albino rats are reared in cyclic light, a burst of rod outer segment disk shedding occurs in the retina soon after the onset of light. The number of large packets of outer segment disks (phagosomes) in the pigment epithelium at this time is 2.5 to 5 times greater than at any other time of day or night. The subsequent degradation of large phagosomes to smaller structures within pigment epithelial cells proceeds rapidly. The burst of disk shedding follows a circadian rhythm for at least 3 days, since it occurs in continuous darkness at the same time without the onset of light.