Presentations of malignant lymphomas in the past did not have the benefit of modern developments in immunology and do not bear any relationship to our modern understanding of immunology. The malignant lymphomas in our immunologic approach are regarded as neoplasms of the immune system and involve principally the T- and B-cell systems and alterations in lymphocyte transformation. The cytologic types of our new classification are an attempt to identify specific functional subtypes of the T- and B-cell systems as defective expressions of their normal counterparts. The results of our multiparameter studies on large case series of non-Hodgkin's lymphomas and those of others have demonstrated that the malignant lymphomas for the most part mark as T- or B-cell types, with the exception of a rare lymphoma of true histiocytic type and the unmarked portion of acute lymphocytic leukemia (ALL) of childhood. They have demonstrated the heterogeneity of the cytologic types of the past that possibly account for the diversity of their clinical manifestations and responses to therapy. The immunologic approach has permitted the identification of homogeneous cytologic types that are emerging as clinical morphologic immunologic entities.