*Institute of Pathology, University of Kiel

Conventional light and electron microscopic methods do not allow a differentiation of T and B-cells. A classification of neoplastic lymphatic cells into one of these subpopulations is therefore impossible with common morphological methods. It was not until specific cell funktions, i. e immunoglobulin(IG)-production and the formation of surface-Ig(S-Ig)receptors, were demonstrable that one could identify B-cells and thereby distinguish them from T-cells. The demonstration of Ig-production therefore represents a method which reveals more information about the nature of malignant lymphoma cells.