In order to validate the use of heart rate (HR) in describing and monitoring physiological demands during soccer activities, the HR versus oxygen uptake ( V(.)O(2)) relationship determined on the field during soccer-specific exercises was compared to that found in the laboratory during treadmill exercise. Seven male amateur soccer players [mean (SE), age 25.3 (1.2) years, body mass 72.9 (2.1) kg, stature 1.76 (0.03) m] performed three trials on the field (two laps of a purpose-made circuit including a variety of soccer activities) at different intensities (moderate, high and very high, according to their rate of perceived exertion) and an incremental test on a treadmill in the laboratory. HR increased linearly with V(.)O(2) during both field and laboratory tests according to exercise intensity ( P<0.01). The mean correlation coefficients of the HR- V(.)O(2) relationships obtained in the laboratory and on the field were 0.984 (0.012) and 0.991 (0.005) ( P<0.001), respectively. The mean value of the HR- V(.)O(2) regression equation slope and intercept obtained in laboratory [0.030 (0.002) and 79.6 (4.6), respectively] were not significantly different compared to those found on the field [0.032 (0.003) and 76.7 (9.7)]. The present study seems to confirm that HR measured during soccer exercises effectively reflects the metabolic expenditure of this activity. Thus, with the aid of laboratory reference tests, the physiological demands of soccer activities can be correctly estimated from HR measured on the field in amateur soccer players.