Whether or not whole blood lactate concentration is the same during a ramp exercise test in subjects with sickle cell trait (AS) as in normal subjects remains a point of controversy in the literature. Some studies have shown that the ability to produce or clear circulating lactate might differ between AS and subjects with normal haemoglobin (AA). If this is indeed so, the lactate distribution in the blood compartments should also differ. To test this hypothesis, lactate concentrations in the whole blood, plasma and red blood cells of AS and AA were compared at rest and in response to exercise. Eight AS and 8 AA performed an incremental exercise test. Whole blood, plasma and red blood cell lactate concentrations, the red blood cell : plasma lactate concentration ratio, the plasma-to-red blood cell lactate gradient, haematocrit and cardiorespiratory variables were analysed at rest and during an incremental exercise test and active recovery. Maximal oxygen uptake and ventilatory thresholds were similar in the two groups. No significant difference in whole blood, plasma or red blood cell lactate concentrations was observed between the two groups at rest, during exercise, or during the immediate recovery. Neither the red blood cell : plasma lactate concentration ratio nor the plasma-to-red blood cell lactate gradient differed between groups. Lactate distribution in the blood compartments did not differ between the two groups and this finding suggests that lactate production and/or clearance is quite similar during exercise in AS and AA.