Two tubes (3 mL each) of whole blood will be collected in the Johnson or DeBakey VA Medical Center by the laboratory services personnel and processed to the freezer (-80 C) within 3 hours from collection. One tube will be collected and allowed to clot. Serum will be separated from this clot by centrifugation (10 minutes at 3,000 rpm) and frozen at -80 degrees centigrade until analyzed. Serum will be used to measure complement factor H activity. The other tube will contain dipotassium ethylenediaminetetraacetic acid (EDTA), resulting in a final EDTA concentration of 4.5 mM when the blood is added. Plasma will be separated from this whole blood by centrifugation (10 minutes at 3,000 rpm) and frozen at -80 degrees centigrade until analyzed. Plasma will be used to measure complement breakdown products. The cells that remain will be used for genotyping assays.