The influence of microwave radiation in millimetre range on the eye has not been investigated so far. However, it is known that microwaves of different wave-length can induce the development of the cataract. Therefore the purpose of the study was to investigate light transmission through the lens after exposure to microwave radiation in millimetre range. The studies were carried out on 22 rats exposed to microwave radiation of 5.6 mm length and power per unit area 10 mW/cm2 or 1 mW/cm2 during 58 days. Light transmission through the isolated lenses was measured spectrophotometrically. Transmission through the lenses was significantly decreased (about 33%) in the rats exposed to microwave radiation of 10 mW/cm2. The results of the study indicate that also microwave radiation in millimetre range can induce changes in the lens, predisposing to cataract development.