The fitness of 8 Andalusian horses between 3 and 4 years of age was analysed. The animals were subjected to an exercise test on a sandy track consisting of 2 stages of different intensities. The first stage was of submaximal intensity at 4 speeds which increased progressively (4.17, 5.56, 6.94 and 8.33 m/sec.) covering a distance of 1,000 m in each level. Between each of these speeds, the horses rested for 2 min. The second stage was a maximal speed test over the same distance carried out 2 min after the ending of the maximal phase. Data of heart rate, plasma lactate concentration, velocity, PCV and pH in the blood were obtained. Maximum heart rate, maximum velocity, VLA2, VLA4, peak lactate, minimum pH and maximum PCV were considered functional indexes. A principal component enabled us to segregate horses according to their fitness and in relation to the information provided by the trainers in charge of these horses. The most discriminant variables in order to segregate horses were pHmin, VLA4, HRmax, VLA2 and Vmax. Differences between horses in relation to PCVmax were not found. The influence of each one of these functional indexes on the test exercise tolerance was discussed.