1. The results obtained concerning the testis, thyroid gland, and anterior lobe of pituitary of the same chickens used in the previous report are described here. In addition, the effects of TPA itself were proved repeatedly in Exp. III in which the doses of TPA were 0, 0.5 and 1.0% in the basal ration, free from the other food additives, i. e. pyrimethamine, prophylactics of coccidiosis and antibiotics, and in which the experimental period was for twenty days and twenty four days beginning from the third day after hatching.<br>2. The testes of chickens treated with TPA decreased in weight (Exp. I). Concerning the histological figures (Exp. II. III), swelling, hydropic degeneration, atrophy or destruction of the interstitial cells were noted, and the falling and disordered multiplying of epithelial cells into the cavity, the appearance of syncytial giant cells and secondary spermatocytal giant cells were observed in relatively many parts of seminal tubules. The epithelial cells fallen into the cavity degenerated before long. But these abnormal views of testes recovered gradually during the later half of the experimental period.<br>There was a delay in spermatogenesis also. The degree of the above abnormities, the delay in recovery from the abnormities and the delay in spermatogenesis corresponded with the dose of TPA, but at the 60th day there were few differences among all experimental groups.<br>3. In the follicles of the thyroid gland, a decrease in height of epithelia, an increase in size of follicles, and a decrease in figure of apocrine secretion were observed. In the early period of the treatment, many epithelial cells had fallen into atrophy, pyknosis and destruction, but they recovered from these abnormities gradually (Exp. II). Vacuolyzation with pyknosis of epithelial cells which was caused by the stagnant colloid was noted in the lot treated with 1.0% TPA in Exp. III.<br>4. In the anterior lobe of the pituitary, not a few δ-cells were atrophic and pyknotic and contained hyaline vacuoles in the lot of 0.5% TPA, and these conditioner were observed to be very extreme in the views of the lots of 1.0% and 2.0% in Exp. I. In these latter two lots a very remarkable appearence of drop-shaped substances strongly dyed with acid fuchsin was noted. A delay in development of δ-cells corresponded rather closely with the dose of TPA in Exp. II.<br>5. The α-cells in the anterior lobe of the pituitary had a tendency to increase in size and number with TPA treatment, and in considerably many birds there were markedly hypertrophied cells which lost their acidophilic granules. In the lot of 1.0% and 2.0% in Exp. I, very many α-cells fell into atrophy and pyknosis, and their granules hyalinized or agglomerated.<br>6. The kidney, adrenal gland and liver in Exp. III had almost the same changes as in the preveous report, i. e. glomerulonephritis and nephrosis in the kidney, hypertrophy of the cortical tissue in the adrenal gland, and an increase in number of degenerated hepatic cells in the liver, and the harmful actions of TPA when an overdose was treated to chickens were reaffirmed by this trial.<br>7. From the above results, it is thought that TPA has the effect of producing castration in chickens though it is temporary, and also has the effect of producing slight hypothyroidism. Thereupon TPA may be used as a food additive for broilers if the dose is appropriate because of its promoting action for the gain of body weight recognized by Tasaki (1964).