In an epidemiologic investigation of the eyes of 209 glass workers with occupational exposure to infrared (IR) radiation and 298 non-IR-exposed controls, the two eyes were compared regarding the degree of lens opacities. The left eye was found to be the most affected in a significantly larger number of persons than the right in IR-exposed workers. The exposure to the two eyes was measured with a system of two pyroelectric radiometers monted in a face mask. The left eye was found to be exposed up to 2.3 times as much as the right in some working moments and never less. These results show a dose-effect correlation between IR-exposure and cataract.