Adequate data from adult ring doves show that the [female] of these forms have longer intestines (5-10%) than the [male]. The presence of Ascaridia is here associated with increased length of intestine in both sexes. Some new data for pituitary size in pigeons of both sexes agree with earlier data (McCarrison) in indicating that in these animals the [female] have larger pituitary glands. The few items of adequate data now available for man, rat and bird lead to the conclusion that there is a sex difference in both pituitary size and intestinal length, and that this difference involves a larger pituitary (particularly anterior lobe) and a longer intestine in the [female]. Some biological and clinical applications of these results are suggested.