The influence of the storage temperature at 20℃ on the biochemical and structural changes in the red porcine muscles (M. cleidomastoideus) postmortem were studied. The results obtained were summarized as follows: 1. 45 minutes to 1 hour postmortem the pH-value had already dropped to 6.4-6.3, after 5 or 6 hours at 20℃ it had reached its final pH-value (5.6). 2. The cause of the rapid glycogenolyses was the fast turnover of ATP. Within 3 hours postmortem ATP had already reached a concentration of about 1μuMol/g muscle. At this level of concentration at 20℃ rigor mortis sets in. At this point most of the glycogen had already been broken down. 3. The irreversible loss of extensibility, i.e, the onset of rigor mortis, arose at 20℃ between 1 and 2 hours postmortem at pH 6.2 to 6.1 and R-value between 1.00 to 1.05. The complete loss of extensibility was reached after 5 hours at pH 5.9. 4. At 20℃ the shortening of the sarcomeres reached approximately 40%. 5. The viscosity of salted homogenates increased considerably as the pH fell below 6.1 and at R values above 1.1.