Summary. The main diagnostic features of leukaemic reticuloendotheliosis (LRE) are discussed in the light of six patients studied in recent years. A detailed study of the clinical, cytological, cytochemical and histological findings in four cases is presented. Pancytopenia and the presence of mononuclear ‘hairy’ cells in the circulation were the main haematological features. Bone marrow was difficult to aspirate and contained 50–80% of the same abnormal cells as the blood; the reticulin pattern showed increased fibre density. The cytology of the LRE cells was very characteristic, particularly because of their irregular ‘hairy’ edges. Cytochemically they were positive for acid phosphatase (tartrate‐resistant) and PAS and they did not contain lysozyme. Electron‐microscopy demonstrated the irregular cytoplasmic edges and a large ‘ribosome‐lamellae’ complex in 25–30% of cells of the two cases studied. The differential diagnosis of LRE from other lymphocytic and histiocytic proliferative disorders is discussed. It is suggested that LRE should be included in the lymphoproliferative group of disorders.

Splenectomy seems to have a definitive place in the management of this condition; three patients out of six did not have splenectomy and died in less than 2 yr of sepsis or haemorrhage; in the other three cases splenectomy was followed by a prolonged improvement in the pancytopenia and a better survival (3 +, 7 and 10+ yr).