An accurate histopathologic diagnosis and classification will be provided for all patients with malignant lymphomas and related leukemias seen at or referred to Stanford University Medical Center (SUMC) including all those entered on clinical trials or biological studies. Fresh tissue or cells from all lymphomas, related leukemias and relevant normal, hyperplastic and other neoplastic tissues from Stanford patients as well as samples from patients at other institutions will be received, appropriately handled for diagnostic and research needs, catalogued, banked and retrieved by technical staff as needed for distribution to all of the project investigators. For project 1 we will prospectively study BCL-6 mutations in PTLD patients using a modification of the SSCP methods as well as sequence negative cases, determine the clonality, the presence or absence of Epstein-Barr virus (EBV), and generate an immunophenotypic profile. We will also evaluate the quantitation of Epstein-Barr viral genomes as a tumor marker by measuring the viral burden at diagnosis, in response to reduced immunosuppression and in response to antibody therapy or chemotherapy. For project 2 we will evaluate the diagnostic potential of gene expression patterns in mycosis fungoides/sezary syndrome (cutaneous TG-cell lymphoma) as well as study the progression of mycosis fungoides/Sezary syndrome (cutaneous T-cell lymphoma) by DNA microarray analysis. For project 5 we will study the progression of low grade follicular lymphoma to aggressive diffuse large B-cell lymphoma as well as study the progression of low grade follicular and other non-Hodgkin's lymphomas to Hodgkin's lymphoma by DNA microarray and microdissection.