1.Four experiments were carried on with a total of 113 chickens to determine whether or not the presence of intestinal worms, Ascaridia lineata (Schneider), had any effect upon the size of the thyroid glands.
2.No significant difference in the size of the thyroid glands of growing chickens was found as a result of the birds being parasitized three weeks with the intestinal roundworm, Asc. lineata.
3.The results of the first, third and fourth experiments showed that the relative size of the thyroids of the females was somewhat larger in the parasitized female birds than in the control females, but the difference did not prove to be significant.
4.Comparisons of the right and left thyroid lobes showed variations in size, but the variations were not constant.
5.No histological changes in the thyroids were found following parasitism with this intestinal roundworm.