The structural changes of intact and laser treated connective tissues were investigated by differential scanning calorimetry and thermomechanical analysis. Total collagen denaturation in the fibrous connective tissue was observed. Partial collagen denaturation in the cartilage tissue was proved. By means, of enzymatic digestion it was shown that proteoglycans in the cartilage act as thermal stabilizers of the collagen, after their removal collagen denatures completely. (C) 2004 Published by Elsevier B.V.