The present investigation aims to ascertain the role of vitamin C upon thyroidal activity in immature pigeons. Thyroid follicular function was assessed by karyo-dynamic and histometric studies. Administration of vitamin C increased mitotic figures as well as epithelial thickeness in the follicles in both sexes of the birds. It is suggested that vitamin C has a mitosis inducing action upon the thyroid gland in juvenile pigeons. © 1979, International Society of Histology and Cytology. All rights reserved.