The red cell mass, splenic red cell pool, and plasma volume have been measured in a series of 64 patients with splenomegaly due to haematological disorders. In 45 patients the total blood volume was increased, this being due to expansion of the plasma volume which was closely correlated with spleen size. There was no significant relationship between the red cell mass and spleen size but the splenic red cell pool increased with increasing spleen size. In 12 patients serial estimations were made whilst changes in spleen size occurred as a result of therapy or progression of the disease. The red cell mass did not alter but the splenic red cell pool showed a significant change from 8·9 ± 6·1% of the red cell mass at minimum spleen size to 17·5 ± 10·5% at maximum spleen size. There was progressive expansion of the plasma volume from 42·9 ± 5·0 ml/kg at minimum spleen size to 57·4 ± 15·3 ml/kg at maximum spleen size.

The splenic pool size has been measured in 50 patients with splenomegaly due to myelo- and lympho-proliferative disorders. Splenic pool size was related primarily to spleen size and was not significantly influenced by the pathological disorder. Changes in spleen size due to treatment or progressive disease altered the pool size. The splenic pool could be discharged with adrenaline and noradrenaline.