Changes in membrane surface receptors have been demonstrated by rosetting methods in polymorphonuclear leukocytes obtained from the pustules of different infectious dermatoses. There was a distinct difference in numbers of receptors in neutrophils from bacterial and viral pustules, i.e., C3b receptors were decreased on neutrophils from both bacterial and viral pustules, whereas IgG-Fc receptors were decreased only in neutrophils from viral pustules. The difference appears to be due to variations in the defence mechanisms against the invading micro-organisms.