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1. Splenic blood flow and splanchnic haemodynamics have been studied in twenty patients with splenomegaly due to blood dyscrasia or diseases involving the reticuloendothelial system. Thirteen of these patients had portal hypertension, three had abdominal collaterals on arteriovenography and one oesophageal varices. 2. Total spleen blood flow was increased in all with values up to 1550 ml/min, and associated with this liver blood flows increased up to 2·61 1 min−1 m−2. In four patients the cardiac output was raised. 3. In five patients a raised wedged hepatic vein pressure was found which was solely related to the increase in liver blood flow, but in two others, in whom hepatic histology was abnormal, there was also an increase in postsinusoidal resistance. Nine patients had a raised hepatic pre-sinusoidal resistance. This was related to a greatly increased liver blood flow with portal tract fibrosis and cellular infiltration as possible additional factors. 4. The haemodynamic findings in these patients were similar to those found previously in patients with tropical splenomegaly. In both groups spleen blood flow in ml 100 g−1 min−1 was inversely proportional to spleen size. There were similar increases in total spleen and liver blood flows and in the percentage of patients with an increased pre-sinusoidal resistance. In contrast, in cirrhosis there was no inverse relationship between flow in 1 100 g−1 min−1, and of spleen size, and for the degree of splenomegaly total spleen blood flow was relatively greater.

The occurrence and causes of a haemodilution anaemia have been studied in two groups of patients, one with diseases of the blood or reticulo‐endothelial system, the other with cirrhosis. In the blood dyscrasia group 37 of 46 patients were anaemic but only 3 had a reduced red cell mass. In the remainder the plasma volume was increased to a greater extent than the red cell mass which was slightly elevated or within the normal range. A significant correlation was found between a decrease in haemoglobin concentration and an increase in plasma volume. Both the increase in plasma volume and the changes in red cell mass were related to enlargement of the spleen. Measurements carried out at splenectomy showed that an excess of red cells was held within the enlarged spleen whereas up to 30 per cent only of the excess plasma could be found there. A correlation between the plasma volume and spleen blood flow was found but both are related to spleen size and the most likely explanation for the increased plasma volume was a primary increase in vascular capacity. The different effect of posture on the plasma volume in patients before and after splenectomy would also support this hypothesis. In contrast, 20 of the 50 cirrhotic patients were anaemic and seven of these had a reduced red cell mass. In the other 13 patients the plasma volume was increased to a greater extent than the red cell mass but even in those with a haemodilution anaemia, the haemoglobin concentration was not inversely related to the plasma volume. In seven patients the increase in plasma volume was less than that of the red cell mass and four patients were polycythaemic. There was no correlation between the changes in red cell mass and plasma volume or between either of these and the enlargement of the spleen. The presence of portal hypertension appeared to be an important factor but the increase in plasma volume was not related to the extent of the portosystemic venous collaterals.