Production of cataract in albino rats placed on a diet deficient in riboflavin (vitamin G, or B2) was first reported by Day, Langston and O'Brien1 in 1931. Confirmation of these results has been obtained by O'Brien2 and Yudkin.3 Langston, Day and Cosgrove4 were able to produce this form of cataract in albino mice, and Langston and Day,5 in Norway rats. Langston and Day6 found that development of cataract in albino rats was arrested when vitamin G was supplied in the form of skim milk powder. The diet used by these investigators in this work on cataract was the "vitamin B-complex deficient diet" of Sherman and Spohn,7 modified by incorporating an 80 per cent alcoholic extract of rice polish.1 The incidence of cataract was consistently close to 100 per cent, the average time of appearance of the cataract being about ten weeks.