Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8) is a blood-borne virus that is etiologically associated with Kaposi's sarcoma (KS), primary effusion lymphoma which is a form of non-Hodgkin's lymphoma, and a subset of multicentric Castleman's disease which is a lymphoproliferative disorder. The investigators developed serologic assays to measure antibodies specific to KSHV latent and lytic antigens. Antibodies to KSHV antigens are found in 70-100 percent of all clinical forms of KS patients. In contrast, relatively low prevalence (2 to 5 percent) is found in the general population of North America. Seroconversion is detected prior to KS onset in AIDS-KS patients, suggesting that primary KSHV infection occurs predominantly in adulthood and is not ubiquitous. Antibody titers to KSHV antigens remain elevated for years after seroconversion. The investigators have recently found a 5 percent prevalence of KSHV infection in blood donors from San Antonio. Further, KSHV has been found in the peripheral blood mononuclear cells (PBMC) of blood donors, and organ transplantation and animal studies have provided evidence of likely person-to-person transmission of KSHV. Thus, KSHV is a potential candidate for screening in blood and plasma donors in view of its etiologic role for several malignancies, low but appreciable prevalence in the general population, and lifelong persistence in a cross-sectional study in blood donors from Texas.