PROTOCOL OUTLINE: Patients are studied systematically to determine the extent of their immune deficiency and to confirm a specific diagnosis. Patients with a known immunodeficiency syndrome are studied in detail to identify the gene mutation, to assess the effect of the mutation on the gene product, and to establish cell lines for further in vitro assessment of the genetic defect. The function of Wiskott-Aldrich syndrome proteins (WASP) in hematopoietic cells is studied.