A bicompartment model has been proposed to describe the distribution of lactate between the active space—muscles—and passive space —plasma and red blood cells—. This transport could be conditioned by the possible existence of a membrane-carrier, blood pH, the concentration of several hormones, the haematocrit value and the haemoglobin concentration. The purpose of this study was to determine the influence exercised by some haematological parameters in the lactate transport between plasma and red blood cells. Twelve male 4-year-old Andalusian horses were subjected to an exercise test, composed of 5 bouts at 4, 5, 6, 7 and 8 m/s, over a distance of 1, 000 m at each level. The horses were given a 3 min. rest between each bout. Venous blood samples were collected at rest, on finishing each level of exercise and at 6, 10, 15 and 30 min of an active recuperation. In blood, pH, RBC, PCV, Hb, MCV, MCH and MCHC were determined. Lactate concentrations were analyzed in plasma and hemolysed blood. Other indices, such as V_LA4 (Velocity at a lactate concentration of 4 mmol/l), Rtd (Rate of lactate disappearance) and ΔLA (Increase in lactate concentrations) were calculated. The highest lactate concentrations were found inside the erythrocytes. The lower values corresponded to plasma, whilst the mean concentrations were observed in hemolysed blood. These differences were only significant at rest and at the two initial levels of exercise. As a consequence, there were found significant differences between V_LA4, Rtd and ΔLA determined in the three media. A positive correlation between blood lactate, PCV, Hb and RBC and a negative correlation to pH were observed. Plasma and erythrocyte lactate showed a negative correlation to pH. Finally, intraerythrocyte lactate was positively correlated to MCH and MCHC.