Ambient light appears to play a role in regulating gene and protein expression of interphotoreceptor retinoid-binding protein (IRBP), a protein that facilitates the transport of retinoids between the neural retina and pigment epithelium in the visual cycle. Pregnant CD-1 mice were placed in the dark approximately 48 hr before parturition, and the pups were reared for 14 days under these conditions. Control animals were reared on a 12 hr light/12 hr dark cycle. Northern blotting of total RNA isolated from whole mouse eyes at post-natal days 7-14 (P7-P14) showed a marked reduction in IRBP message in the light-deprived animals to 10-20% of levels in control animals. Reprobing of the blots for opsin and S-antigen message showed a significant decrease of about 80-90% in opsin message at 5.1 kb but no change in S-antigen message in the eyes of light-deprived mice. Light microscopic examination of the light-deprived mouse retinas showed no apparent abnormalities in morphological development and immunocytochemistry demonstrated normal distribution and levels of IRBP protein. Immunochemical quantitation of IRBP protein confirmed that there was no reduction in light-deprived as compared to normal mouse eyes. Similarly, when adult mice were light-deprived for 14 days, a marked reduction in IRBP message was also observed with no decrease in the amount of IRBP protein. Thus, light deprivation causes a large decrease in IRBP message in the mouse eye, but IRBP protein is not decreased. The dramatic effect of light deprivation on IRBP mRNA and some opsin mRNAs, but not on S-antigen message and the fact that IRBP protein levels are relatively unaffected, suggest a complex pathway of light regulation of photoreceptor function previously not encountered. This may involve regulatory controls at levels including gene transcription, mRNA stability or protein degradation that may make use of a feedback control mechanism involving light- or dark-dependent signal transduction.