Here we report the first results of combined scanning calorimetric and dilatometric investigations carried out on bovine serum albumin in aqueous solution at 30-97°C. Comparison of experimental data obtained by the two techniques suggests a "steps" model for the thermal denaturation of the protein. Moreover, the results in the high-temperature region, after aggregation of the unfolded chain, show a subsequent, previously unreported, spatial rearrangement of the polypeptidic chain network, during which the order of the system increases with an increase in temperature. The results indicate that scanning dilatometry is a very useful method of detecting phenomena which are not seen by calorimetry. The results also demonstrate the determinant role of water in the unfolding process. © 1994.