The contribution of entropy and enthalpy to the chair-boat conformational changes (clicks) occurring during the force-extension of single molecules of an axially linked polysaccharide, dextran, was investigated. Experimental single molecule force-extension measurements were carried out by atomic force microscopy over the temperature range of 5-70 degrees C. This enabled the separation of the entropy and enthalpy components of the conformational change. The contribution of entropy to the Gibbs energy of the conformational transformation was found to be small (< 12 J mol(-1) K-1), demonstrating that the click is largely (> 89%) enthalpic in nature.