Alterations of junctional structures in non‐immune mediated acantholytic diseases (Grover's, Hailey‐Hailey's and Darier's diseases) were examined using monoclonal antibodies against desmosomal attachment constituents (desmoplakin I & II and plakoglobin), desmosomal intercellular cement glycoprotein (desmoglein), protein of adherens junction (vinculin), and protein of gap junction (43Kd connexin). Universal cell surface (transmembrane) glycoprotein CD44 was also studied. In acantholytic foci of these diseases, attachment plaque proteins had dissolved and diffused into the acantholytic cells. The normal dotted linear pattern of immunostaining on the cell membrane was totally lost. In contrast, CD44 was well preserved on the cell membranes of acantholytic cells. Adherens junction and gap junction proteins were mostly preserved. Acantholytic cells of pemphigus vulgaris were similarly studied. In these cells, desmosomal attachment plaque proteins were very well preserved, while intercellular cement substance (desmoglein), adherens junctional proteins (vinculin), and gap junction protein (connexin) were totally absent, either on the cell membrane or in the cytoplasm. Electron microscopy confirmed an early dissolution of attachment plaque. Internalized desmosomal structures were seldom found in acantholytic cells of non‐immune diseases. It was concluded that the primary event in acantholysis in these three diseases is the dissolution of desmosomal attachment plaque.