Physiological responses of a group of 16 tennis players have been investigated under the almost natural conditions of a 10 min long training match. Collecting the expired air into Douglas bags, transmitting heart rate all the time of experiment wirelessly and analysing every player's activity we have got following main results: The average intensity of metabolism was 919.5% BMR, that is 0.14 kcal per min and kg of body weight. The oxygen uptake have been found 27.3 mlO2/min·kg, while the mean heart rate during the match was counted as 143 beats/mm. It was found, too, that players ran totally 240 m, executed in average 62 strokes and used 41.1% of the total time for real play. With regard to our results tennis can be grouped together with bicycleball and American handball, while basketball, European handball, soccer and ice-hockey on one hand, and Volleyball with table-tennis on the other hand, differ significantly. There was also found significant difference between caloric output in recreational and competitive type of tennis game. Our investigation then can support the view tennis means the submaximal load for players mainly.