Caliber irregularities of the small retinal vessels may usually be observed as an early sign of vascular disturbance in young cigarette smokers. A randomized blind study on 28 smokers and 30 non-smokers aged between 17 and 39 years, which were entirely healthy according to the results of physical and ophthalmoscopical examination, was undertaken with the aid of fluorescence angiography. Only smokers with a consumption of at least 15 cigarettes daily and a history of smoking of at least 5 years were taken into account for the study. The angiograms were read as fluorescein angiographic negatives under a stereomicroscope. To the person interpreting the angiograms, name or date of the angiograms were not know. Caliber irregularities of the retinal arteries, veins, arterioles and venoles were found in 18 of the smokers and 2 of the non-smokers. The incidence of vascular irregularity in smokers is highly significant at the 1% level.