The aim of the study was to investigate the distribution of lactate in plasma, whole blood, erythrocytes, and capillary finger blood, before and during submaximal exercise. Ten healthy male subjects performed submaximal graded cycle ergometer exercise for 20-25 min. Venous blood samples and capillary finger blood samples were taken before exercise and every 5th min during exercise for lactate determination. The plasma lactate concentration was significantly higher (P less than 0.001, approximately 50%) than in the erythrocytes. This difference was not altered by the venous blood lactate concentration or exercise intensity. A significant difference (P less than 0.01) in lactate concentration was also found between capillary whole blood and venous whole blood. It was concluded that direct comparisons between lactate in capillary finger blood, venous whole blood and plasma could not be made.