RAPID AND SEVERE DESTRUCTION Of periodontal tissues in early childhood has been reported both in systemically healthy children and in children with systemic disorders. In this study, the clinical and immunological findings of two siblings in a family with Papillon-Lefevre syndrome are presented. The peripheral blood lymphocytes were analyzed using a double colored flow cytometry and adequate monoclonal antibodies to CD2, CD3, CD4, CD5, CD8, CD11b, CD16, CD19, and HLA-DR receptors. CD11b expression was found to be higher in both siblings (35% and 37%). The elevated CD11b expression may be related to a defect in neutrophils. The expression of natural killer cells was found to be higher in one patient but the results were in normal range. The CD2+, CD3+, CD4+, CD5+, CD8+, and CD19+ lymphocytes were in normal range in both patients. We think that the depressed chemotaxis of peripheral neutrophils, and higher expression of HLA-DR and CD11b molecules in peripheral leukocytes were useful in explaining the pathogenesis of the Papillon-Lefevre syndrome.