The fat body bacteriocytes of Periplaneta americana can be cultivated in an hormone-free culture medium. Endocytobiotes break down after 48 hours in culture and develop into residual bodies or into cytolysosomes after 8 days. The addition of ecdysone does not prevent the endocytobiote lysis whereas the co-culture of fat body and corpora allata has a beneficial effect. For the first time endocytobiotes were maintained in vitro under the hormonal induction of corpora allata. Furthermore ,the data presented suggest that endocytobiotes and mitochondria seem to interact during the in vitro culture.