week laying hens were fed with high iodine diets for 16 weeks.Observations were made on egg production, fertility and hatchability.The concentrations of estrogen and progesterone in the plasma were measured by radioimmunoassay.Com pared to those in the control group.the egg production of hens fed high dietary io dine were obviously lower at the end of the experiment.No significantdifference was observed in fertility but hatchability decreased with the increasing dietary ioding.The basal lever of estrogen in plasma showed little changes while the basal progesterone level increased significantly,and the secretion of estrogen and progesterone during the ovulatory cycle showed abnormality with high dietary iodine.