Histiocytic cytophagic panniculitis presents with subcutaneous panniculitis. Histologically, it is characterized by phagocytosis of blood cells in the subcutaneous tissue and bone marrow. One patient with histiocytic cytophagic panniculitis is described in whom hemophagocytosis macrophages and histiocytes was observed histologically and was confirmed in vitro measuring phagocytosis by peripheral blood monocytes by means of chemiluminescence. In vitro measurements of phagocytosis corresponded well with the clinical course. Chemiluminescence for measuring phagocytosis in vitro may be suitable for analyzing disease activity and for testing therapeutic compounds in vitro.