As diabetic retinopathy progresses, the non-perfused area in the retina gradually enlarges as the capillaries are obstructed. To elucidate the process of capillary obstruction we examined macular capillaries in 104 diabetics, using fluorescein angiography. The follow-up period was three to eight years. We found that some capillaries in the macular were obstructed, then became unobstructed. Reflow of blood into the macula after the obstruction was observed in nine patients (8.7%). The time between obstruction and reflow varied from two months to four years. There were four cases of simple, three of preproliferative, and two of proliferative retinopathy. Reflow in the capillaries was confirmed as occurring at the same position and in vessels with the same diameter as seen before the obstruction. There was no leakage of the fluorescein dye from the capillary where reflow took place. We tentatively conclude that one of the causes of this phenomenon is a functional obstruction.