The Achilles tendon rupture is a common injury of the foot in middle age and physically active population in Europe. The aetiology of the degenerative changes in the collagen structures of the tendon which could be disposed for the rupture is still not clear. Our hypothesis was that before the injury there is a clear pathological abnormality in the tissue elements building up the Achilles tendon, which is responsible for the disease, and could be monitored besides the classical histological methods by differential scanning calorimetry. The thermal denaturation of human samples was monitored by a SETARAM Micro DSC-II calorimeter. All the experiments were performed between 0 and 100 degrees C. The heating rate was 0.3 K/min. DSC scans clearly demonstrated significant differences between the control and ruptured samples (control: T-m = 59.7 degrees C, T-1/2 = 1.4 degrees C and Delta H-cal = 8.54 J/g; ruptured: T-m = 62.75 degrees C, T-1/2 = 2.6 degrees C and Delta H-cal = 1.54 J/g). These observations could be explained with the structural alterations caused by the biochemical and structural processes. With our investigations we could demonstrate that DSC is a useful and well applicable method for the investigation of collagen tissue of the human Achilles tendon. We can prove with this method, that the earlier series of microtraumas which result a scar formation in the tendon tissue increases the thermal stability of collagen in ruptured tendon. (C) 2009 Elsevier B.V. All rights reserved.