Absence of the choriocapillaris (CC) was observed histopathologically in human eyes with retinitis pigmentosa (RP). It was noted in areas where the overlying retinal pigment epithelium (RPE) was absent. Analysis of our material, as well as a review of the literature dealing with RP and related entities, as well as a number of other fundus disorders, suggested that the disappearance of the CC is secondary to REP degeneration. An experimental model using intravenous sodium iodate produced a similar sequence of events in the rabbit. We suggest that the RPE modulates structure and function of the CC. There is possibly a diffusable biochemical vascular modulation factor (VMF) which is required for normal CC fenestrae formation and maintenance, which is liberated by the normal RPE, and acts upon the vascular endothelium. Lack of VME causes the endothelium to lose its fenestrae and the vessel to occlude. This RPE-CC interaction is a further facet of the RPE which requires exploration in depth.