A method is described for the estimation of serum haemoglobin binding capacity. The method is based on the separation of the high molecular weight haemoglobin . haptoglobin complex formed after addition of haemoglobin in excess to serum from uncomplexed haemoglobin by gel filtration through Ultrogel AcA 44. Agar gel electrophoresis and benzidine staining proved that the first fraction was exclusively the haemoglobin . haptoglobin complex. The second peak consisted of free haemoglobin. In this method the amount of haemoglobin bound to haptoglobin is calculated from the absorbance of the chromatographed complex at 412 nm. The results obtained are reproducible and comparable with those of an electrophoretic reference method, but less precise. The method is simple, and accurate, and is faster than gel filtration methods described earlier.