Acute exposure of ultraviolet radiation to the cornea has previously been shown to produce endothelial pleanorphism and polymegethism. The reciprocity of exposure intensity and duration typically soon with the photochemical effects of ultraviolet radiation on biological tissue predicts a similar effect with chronic exposure. This was tested by comparing the regularity of the hexagonal endothelial mosaic for a group of workers (n=9) chronically exposed to solar radiation to that for an age-matched control group (n=18). Although the mean cell area of the endothelium was similar between groups (p<0.10), a significant difference (p<0.01) was demonstrated in the degree of polymegethism. This supports the contention that chronic ultraviolet radiation exposure may contribute to increased polymegethism seen with age.