Several oral and cutaneous lesions of pemphigus vulgaris were studied electron microscopically. Desmosomes and attached bundles of tonofilaments appeared to be normal in the vicinity of acantholytic bullae, while the intercellular cementing substance was largely dissolved. Whenever the intercellular cement was preserved, the cells in the lesion remained attached to each other, even after a complete disappearance of the desmosome-tonofilament complex. In the oral lesions, serum exudate often filled the intercellular spaces, but not the space between the basal cells and the basement membrane. Abnormal membrane-coating granules were found in abundance in the oral lesions. These might play an important role in the pathogenesis of acantholysis of pemphigus by producing defective cement or substances which might exert a lytic effect on the intercellular cement.