The potential of a series of related compounds to induce haemolytic anaemia in dogs highlighted the need for a reliable and sensitive technique to identify changes in plasma haptoglobin concentration. An indirect method established for human samples was adapted for use with canine plasma. This method measures the haemoglobin binding capacity of plasma, which is directly proportional to the functional haptoglobin concentration. The efficacy of this technique was investigated on samples taken from Beagle dogs which had previously received small quantities of water intravenously. A substantial reduction in haemoglobin binding capacity was recorded before other haematological parameters were significantly affected. It was concluded that measurement of haemoglobin binding capacity by this method provides a valid reflection of haptoglobin status in the dog.