The exercise intensity of horses competing in the cross country phase of an advanced horse trial (Group 1; n=17) and an advanced 3-day combined training event (Group 2; n=7) over a similar course on the same day was investigated. Environmental conditions during the trial were cool. Heart rates were continuously recorded at 5 s intervals by a heart rate monitor. Mean ± s.d. heart rates for Group 1 and Group 2 were 167.7 ± 24.0 beats/min and 171.4 ± 19.2 beats/min, respectively, (P>0.05). Plasma lactate concentrations were determined at rest, within 60 s post exercise and 10 min post exercise. Mean lactate concentrations were highest immediately post exercise (Group 1=15.18 ± 5.79 mmol/l; Group 2=19.10 ± 4.22 mmol/l) and had declined significantly in 10 min (Group 1=11.15 ± 6.56 mmol/l; Group 2=16.06 ± 6.11 mmol/l). Lactate concentrations were not significantly different between groups at each time period. We concluded that the work effort for the cross country phase was not different between advanced horse trial and 3-day competitions for horses competing under similar conditions during non stressful environmental conditions.