SUMMARY: Changes in concentration of a number of blood metabolites in 30 thoroughbred horses were recorded after an 1100 metre race.

No significant changes occurred in blood urea or aspartate aminotransferase during the three hours after racing. Plasma sodium, potassium and calcium levels were increased immediately after racing but had returned to normal one hour after racing. Plasma phosphate showed a significant fall in concentration one hour after racing.

Creatinine and lactic acid concentrations were elevated ten minutes after racing and although they subsequently decreased, the level of lactic acid was still significant one hour later. Uric acid levels were well above resting levels at ten minutes after racing but rose even more in the subsequent hour. Urinary uric acid levels were also elevated during this time.

Three hours after racing some horses still had elevated plasma uric acid levels and all of them showed a significant rise in creatine phosphokinase.

The possible physiological basis of these findings is discussed.