Participating family members will provide a medical history, and their pulse, blood pressure and temperature will be taken. They will have 10 to 120 ml (1/3 to 4 ounces) of blood drawn from a vein in the arm. Blood samples may be taken on repeated occasions as long as the relative remains in the study. The blood will be used for research that may involve development of diagnostic tests for CVI, evaluation of the structure and function of normal blood cells for comparison with those of patients with CVI, and studies to try to determine possible genetic factors involved in susceptibility to CVI.