External application of the dye Lucifer yellow to isolated retinas of Xenopus laevis causes a specific staining of the distal tips of the rod outer segment (ROS). Staining occurs most frequently in the distal 4 micron of the ROS and does not diffuse throughout the ROS cytosol. In contrast, damaged ROS fill with the dye and exhibit a diffuse fluorescence. Retinas from constant light-treated animals show a greater frequency of labeling when isolated in the light than when isolated in the dark after 0.5 and 3 hr. Increased frequency of distal tip staining for dark-treated animals can be achieved if animals are returned to the light. Distal tip labeling also occurs in cyclic-light maintained animals but at a much lower frequency. The frequency of distal tip staining can also be altered by temperature and metabolic poisons. Isolated retinas exposed to dye solutions kept at either 3 degrees C or containing the metabolic poisons, iodoacetate or dinitrophenol, exhibited a reduced frequency of staining. This suggests that staining is an active process involving cellular metabolism. The distal location, dimensions, and light dependence of staining suggests that labeled regions are destined for detachment as part of disc shedding. The sensitivity of distal tip staining to metabolic poisons suggests that the photoreceptor plays a role in determining the membrane domains destined for shedding.