The aim of this study was to examine heart rate, blood lactate concentration and estimated energy expenditure during a competitive rugby league match. Seventeen well-trained rugby league players (age, 23.9 ± 4.1 years; V̇O 2max, 57.9 ± 3.6 ml.kg -1.min -1; height, 1.82 ± 0.06 m; body mass, 90.2 ± 9.6 kg; mean ± s) participated in the study. Heart rate was recorded continuously throughout the match using Polar Vantage NV recordable heart rate monitors. Blood lactate samples (n = 102) were taken before the match, after the warm-up, at random stoppages in play, at half time and immediately after the match. Estimated energy expenditure during the match was calculated from the heart rate-V̇O 2max relationship determined in laboratory tests. The mean team heart rate (n = 15) was not significantly different between halves (167 ± 9 vs 165 ± 11 beats.min -1). Mean match intensity was 81.1 ± 5.8% V̇O 2max. Mean match blood lactate concentration was 7.2 ± 2.5 mmol.l -1, with concentrations for the first half (8.4 ± 1.8 mmol.l -1) being significantly higher than those for the second half (5.9 ± 2.5 mmol.l -1) (P < 0.05). Energy expenditure was approximately 7.9 MJ. These results demonstrate that semi-professional rugby league is a highly aerobic game with a considerable anaerobic component requiring high lactate tolerance. Training programmes should reflect these demands placed on players during competitive match-play.