Research studies indicate that, by determining the physiological load placed on athletes during competitions, it can aid in the development of strength and conditioning programmes, according to the specific demands placed on athletes. Physiological data, specifically on rugby union players, are limited, thus stressing the need for more information in this area. The aim of the study was to investigate the physiological demands of South African male U/21 club rugby players and to establish the relationship between physiological demands experienced during rugby games and practice sessions. Scientific methods to describe physiological demands in sport that are used are heart-rate and blood-lactate measurements. A group of U/21 rugby players (n=15) of the University of Pretoria (Tuks) rugby club participated in this study. Variables that were tested included blood-lactate concentrations and mean heart-rates during a rugby match and practice sessions. The Tuks U/21 team’s data were analysed by means of descriptive statistics (means and standard deviations). Significant differences between rugby match and practice sessions were determined by a dependent t-test (p<0.05). An independent t-test was used to determine significant differences between the forwards and backs group. The results showed statistically significant differences between mean heart-rate in the rugby match (154.40 ±13.53) and practice sessions (138.33±4.81). No significant differences were found between peak lactate measurements in the match (5.39 ±2.44) and practice sessions (4.93±1.83). Between the forwards and backs group no statistical significance could be found for average heart-rate and blood-lactate levels in practice sessions and during the match. The findings of the present study indicate that rugby union matches for club level U/21 players are an intermittent type of activity, which utilise both aerobic and anaerobic energy systems.