SummaryTo determine whether maximum oxygen uptake (VO2max) in the horse is influenced by type of exercise test, five different protocols were evaluated in eight untrained Thoroughbreds exercised on a treadmill. With all protocols, horses were given a 5 min warm‐up on a 10 per cent treadmill slope. Three protocols were at a 10 per cent slope and included: 1) increasing the running speed by 1 to 2 m/sec every 60 sees from 4 m/sec to a maximum of 12 m/sec; 2) running at 12 m/sec until fatigue; and 3) running for 3 to 4 mins at speeds ranging from 6 to 12 m/sec with rest pauses between exercise bouts. The fourth protocol employed a 24 per cent slope where animals exercised for 5 mins at 2 m/sec followed by 3 mins at 5 m/sec, and 2 mins at 6 m/sec. The fifth test involved running at 11 m/sec while the slope of the surface was increased every 2 mins until the horses could not maintain the pace. A plateau in V̇O2occurred in all protocols except when exercise was performed on a 24 per cent slope. Slow speed exercise at a steep grade (24 per cent) produced the highest V̇O2(P<0.05) even though there was no plateau in the V̇O2. A steady state for V̇O2and V̇CO2existed 90 secs after the onset of exercise with all protocols which involved 2 mins or more at each speed. The V̇O2and V̇CO2values at all speeds of the rapid incremental exercise test were not different to those found at steady state in the third exercise