Eight thoroughbred horses, trained for racing competition, were subjected to a standardised incremental speed test to determine the relationship between their blood lactate concentrations and running speed. Between 14 days before and 14 days after completing the standardised exercise test, the horses were timed for runs of 2000 to 6000 m. The blood lactate concentration after each run was measured and compared with the blood lactate concentration predicted from the individual horse's blood lactate-running speed relationship curve determined from the standardised exercise test. The relationship between the predicted and measured lactate concentrations was evaluated by linear regression. For 42 exercise runs there was a significant positive correlation between the measured and the predicted lactate concentrations and a significant regression: measured lactate (mmol/litre) = 1.01 predicted lactate (mmol/litre) - 0.36 (r2=0.79, standard error of estimate 0.63 mmol/litre, P<0.001). It was concluded that the standardised exercise test was a useful technique for predicting the blood lactate concentrations of horses after field exercise.