After castration the inhibition of female protein production, due to the mature oocytes at the end of vitellogenesis, cannot take place, and female protein synthesis goes on in the fat body. A histological study of the fat body was done after castration of the female ovoviviparous cockroach Nauphoeta cinerea to test this abnormally long lasting production of female protein. Our results show an actively synthesizing fat body even long after castration, this being in total accordance with the biochemical results of the literature.