1. Ionized calcium, protein-bound calcium and total calcium in serum were measured in patients receiving haemodialysis treatment.
2. During dialysis, the ionized calcium fraction decreased and the bound calcium increased. The blood pH also increased.
3. Studies in vitro suggested that the fall in ionized calcium and rise in protein-bound calcium were larger than could be explained by the redistribution of calcium fractions due to the pH change.
4. An explanation could be that haemodialysis increases calcium binding by serum proteins. Such an effect may be implicated in the aetiology of hyperparathyroidism and bone disease in patients undergoing haemodialysis.