Thin sections of methane-utilizing bacteria have been examined in the electron microscope and the fine structure of the cells is described for the first time.The outstanding feature of all the isolates studied is the existence of intracellular membrane structures resembling those seen in nitrifying and photosynthetic bacteria. The possible significance of these membranes is discussed.

Crystalline inclusion bodies resembling those seen in Clostridium cochlearium were detected in cultures of Bacillus thuringiensis infected with bacteriophage.