Observations based on a clinical and experimental study of the effect of hair dye (paraphenylenediamine) on the lens are reported. Two hundred individuals of either sex using hair dye were examined in detail and lenticular changes were found in 89% while only 23% in controls. The lenticular changes were related to duration, amount, and individual sensitivity to dye. Various types of lenticular opacities encountered are mentioned. In addition some individuals (7%) were found to develop early presbyopia. Experimental study which was conducted in rats and rabbits confirmed the cataractogenic effect of hair dye beyond doubt. It is concluded that hair dye is potentially toxic to the human lens.