In Blattella germanica, the German roach or "croton bug," bacteriocytes are found in all individuals of both sexes. These bacteriocytes are scattered throughout the fat tissue and their cytoplasm is filled with microorganisms. Evidence is presented to show that the intracellular parasites are diphtheroidal bacilli. These diphtheroids are transmitted from one generation to another through the ova. By using a technic previously described, the intracellular parasites were isolated and cultivated from the adult bacteriocytes and from embryos. Two diphtheroidal strains were cultivated with approximately equal frequency. These two strains resemble one another closely enough to be considered a single species but show certain minor differences. The sizes, general morphology, and tinctorial reactions of the two cultures correspond to the intracellular parasites of Blattella germanica. They may be distinguished from the three types of Corynebacterium periplanetae variety americana, previously described. For the species here discussed the name Corynebacterium blattellae nov. sp. is proposed.