The process of thermal denaturation of a covalently modified form of barley grain nonspecific lipid transfer protein 1b (ns-LTP1b) was investigated by nuclear magnetic resonance (NMR) and differential scanning calorimetry up to 115 degrees C. The denaturation was found to be irreversible and highly cooperative. A method of numerical quantitative analysis allowing us to fit the NMR data to a transition state model without further simplification was developed. On the basis of the obtained values of transition state enthalpy and entropy, the rate of denaturation was calculated as a simple measure of protein stability at various temperatures. The effect of disulfide bond reduction on thermal denaturation of ns-LTP1b was studied and discussed in the context of quality control of barley products during storage and processing.