Immunological markers important for the diagnosis of the following subtypes of Non-Hodgkin lymphomas (NHL) are discussed: lymphocytic lymphomas (i.e.: B-CLL, immunocytic NHL, prolymphocytic- and hairy cell leukemia), NHL derived from follicular center cells (centrocytic, centroblastic/centrocytic and centroblastic NHL), lymphomas with blastoid appearance (various forms of lymphoblastic and "large cell" NHL) and disorders of T lymphocytes (NHL) of peripheral T cells and T gamma lymphocytosis with neutropenia). In these disorders, the patterns of leukocyte surface antigens like T1 (CD5), Tac (CD25), CALLA (CD10), FMC7, Tü1 and Tü33 as well as staining for the terminal transferase (TdT) and of dendritic follicular cells have been examined by investigating specimens of a large group of patients. Apart from the diagnostical value, these evaluations have contributed to a better understanding of normal B cell differentiation whereas the role of marker studies as independent prognostic factors requires additional prognostic studies. Finally, the value of immunoperoxidase or alkaline phosphatase staining of cryostat sections of bone marrow biopsies is emphasized, which allowed the diagnosis and classification of 74% of 92 NHL studied by this technique.