Rapid-sequence fluorescein angiography was performed simultaneously on both eyes of each of 241 healthy individuals in order to analyze and compare dye inflow patterns in the eyes of each subject. The many uncertainties of successive investigations resulting from uncontrollable changes in systemic circulation parameters between the two angiographies were thus eliminated. In over 90% of the subjects there was no difference between the two eyes in respect of arm-fundus time nor the filling pattern of choroid and retina. A few subjects did show a difference, but this lasted for only one exposure and was normalized on the second exposure of the sequence. It is therefore concluded that side differences of the fluorescein inflow pattern on simultaneous bilateral angiography are highly suggestive of unilateral circulatory disturbances in the cervical, retinal or choroidal vessel. Such disturbances are practically certain if side differences last for more than just one exposure. In contrast, the filling pattern in cilioretinal arteries was very variable and over one third of the subjects presented with side differences between their two eyes. Therefore the filling pattern of these vessels cannot be used for diagnostic purposes.