The effects of castration on the structural variations of the thyroid gland were studied in male buffaloes. Following castration (open method) the diameter of the thyroid follicles was somewhat larger. The percent of high cuboidal (6.5 - 10.5 um) type of follicular cells was greater (48.44%) in the control group, whereas in the castrated group (open method) low cuboidal (3.3 - 6.4 um) type of cells appeared to preponderate (56.08%). The height of the follicular cells was appreciably decreased (P/ 0.01) in buffaloes castra ted by open method. These changes in these emasculated buffaloes were also correlated with a significant decrease in thyroidal uptake of 1 (UT) and percent erythrocyte uptake of 131 1 (EUT). However, no variations were observed in the size of the thyroid follicles, percent and height of follicular cells as also in the values of UT and EUT in the caudectomized animals.