Summary. The clinical and haematological features of 15 patients with a rare variant of chronic lymphocytic leukaemia (CLL) are described. The disease predominantly affects males in the sixth and seventh decades of life and presenting symptoms include fatigue, weakness, weight loss, sweats and fevers. Massive enlargement of the spleen (mean weight at autopsy 1383 g, range 227–3500 g) and to a lesser extent of the liver (mean weight 2445 g, range 2030–3079 g) are regular findings. In contrast, peripheral lymphadenopathy is inconspicuous or absent. The characteristic cell in the peripheral blood is a relatively large lymphoid cell with a large vesicular nucleolus, relatively well-condensed nuclear chromatin and moderate amount of cytoplasm. The counts of these cells in the peripheral blood at the time of diagnosis are very high (mean 355 000/μl, range 26000–1 11 000/μl). The clinical response to methods of treatment that are usually effective in classical CLL (particularly alkylating agents and corticosteroid drugs) is uniformly poor and the patients’survival after diagnosis is in most cases quite short.

We believe that the clinical and haematological features of this condition justify its recognition separately from classical CLL, from lymphosarcoma cell leukaemia and from acute lymphoblastic leukaemia. We have therefore designated it ‘prolymphocytic leukaemia’. On the basis of a single case we suggest that further trials of splenectomy are indicated.