Disorders of the histiocyte-macrophage system in childhood comprise a manifold variety of clinical entities. The basic immunopathological mechanisms have still not been clarified in detail. We report on a 15 months old Yugoslavian boy of non-consanguineous parents, who developed persistent high temperatures and bloody diarrhoea at the age of 11 months, followed by a rapidly progressive dystrophy, hepatosplenomegaly and peripheral pancytopenia. An extensive virological, bacteriological and protozoal diagnostic program failed to reveal a pathological result. A bone marrow aspiration showed an extremely hypocellular marrow without infiltration of pathological cell populations. In spite of extensive supportive care and systemic steroid therapy, the patient died by bleeding complications due to severe untreatable thrombocytopenia. In post-mortem-biopsies a marked infiltration of RES-organs (lymph nodes, liver and spleen) by mature histiocytes, showing marked hemophagocytosis, was seen.