In 8 patients with lymphadenosis benigna cutis (LABC) cytochemical and in 2 of them immunocytological studies have been performed. 1) In patients with LABC we find ectopic organoid proliferations of "lymphfollicle"-like structures within the dermis which predominately consist of small lymphocytes and large reticulum cells. Immunocytological differentiation of the lymphocytes leads to the characterization of B- and T-lymphocytes in a ration 2:1. 2) Large reticulum cells represent a peculiarly remarkable cell class in infiltrates of LABC. Because of their typical arrangement disseminated within the lymphocytic infiltrate they have been designated as "starry sky" cells. Cytochemically they are characterized by an unusual high content of nonspecific esterases and acid phosphatase, most of them show phagocytized basophilic bodies. Because of their shape, arrangement and enzymcytochemical behaviour these cells can be referred to as typical for the LABC disease. 3) Monocytes cannot be found within the "lymphfollicles". Mast cells and connective tissue cells are rarely observed. Polymorphonuclear granulocytes can be demonstrated in great numbers in any part of the involved cutis when there is an insect bite in history. 4) As a reaction of the ectopic proliferation of lymphoreticular tissue within the dermis there is an activation of the surrounding connective tissue with an increase of the alkaline phosphatase activity within these cells, new formation of collagen fibres and strong proliferation of alkaline phosphatase positive capillaries. 5) Etiopathologically it is stressed, that in LABC for example an insect bite induces stimulation of hematopoietic potentialities of undifferentiated mesenchymal germ centres within the cutis takes place, leading to the development of ectopic of "lymphfollicle" like structures.