Leukocyte adhesion deficiency (LAD) is a recently recognized autosomal-recessive trait characterized by recurrent bacterial infections, impaired pus formation and wound healing, and abnormalities in a wide spectrum of adherence-dependent functions of granulocytes, monocytes, and lymphoid cells. Features of this disease are attributable to deficiency (or absence) of cell surface expression of a family of functionally and structurally related glycoproteins. These include Mac-1 (complement receptor type 3), lymphocyte function-associated antigen-1 (LFA-1), and p150,95. Defective biosynthesis of the beta chain shared by each molecule (comprised of alpha 1 beta 1 complexes) represents the fundamental molecular basis of this disease. Recognition of the molecular pathogenesis of this disorder has allowed rich insights into the role of cellular adherence reactions in inflammation and host defense.