The effects of two lathyrogens (beta-aminopropionitrile and semicarbazide) on the reproductive system of the laying hen were compared by measuring the changes in the ovary and oviduct associated with a diminished egg production rate. The laying hens were fed diets containing either beta-aminopropionitrile, the toxic constituent of certain legume seeds in the genus Lathyrus or semicarbazide to induce lathyrogenic effects in which reduced egg production was one of the toxic effects. The gross examination of the reproductive system of the hens revealed that ovarian activity was greatly impaired. The reduced egg production after feeding beta-aminopropionitrile was due to the reduced growth rate of the ovary, and in the case of semicarbazide, to the atresia of large yolky follicles.