In the culture fluids and on the cells of two toxigenic strains of Clostridium novyi type A, bacteriophages were detected and confirmed by electron microscopy (Fig. 1 and 2). The heads of the bacteriophages are hexagonal and 500 A in diameter. The tails have a length of 1400 A and a diameter of 60 A. Reproduction of the bacteriophages was not yet possible owing to the lack of sensitive indicator strains.