WE have in previous papers called attention to the changes in the physiological state of the body especially regarding the respiratory functions at the transition from rest to work and during the initial stages of muscular work either voluntary or electrically induced (1, 2). In the present paper we propose to deal with another transitional state, namely the transition from work to rest. We have made use of Krogh's bicycle ergometer and respiration apparatus described in detail elsewhere(3). After a working period of variable length and intensity the work was stopped suddenly, and the subject placed his feet on the foot-clamps of the ergometer. Thus the experiments after work were made in the same position of the subject as were the resting experiments made before work began and they may be compared directly with the latter. Usuallv the first respiration experiment began about *2 minute after cessation of work and lasted about half a minute, the later experiments lasted a minute or a little more. In addition to the respiration experiments b-samples of alveolar air were drawn corresponding more or less closely to the former. As however the values for the metabolism calculated from the b-samples and the calculated alveolar ventilation differ some 10 per cent. from the results of the respiration experiments, and as the correction to be introduced is not constant owing to the fact that the b-samples to a certain degree depend on the mechanics of respiration, we do not think it of sufficient interest to deal with the alveolar samples, especially, as the results obtained from these on the whole only differ from the results of the respiration experiments in showing a somewhat greater variability. In the following pages the main -results will be dealt with; some protocols are given at the end of this paper to illustrate the details of the experimenta.