In 1998, we published the data compilation PROTEIN STABILITY AND FOLDING which covered the data from the early beginnings of thermodynamic studies of protein folding until 1996. Since then, the amount of available thermodynamic data has increased nearly twice. The data constitute very important additions to the information on the protein folding problem, the construction of mutant protein, and the practical application of proteins in various fields. The Supplement covers the period 1997-1999 and is designed to make the vast amount of present data accessible to multidisciplinary research where chemistry, physics, biology, and medicine are involved and also biotechnology, pharmaceutical and food research. At the same time the data could be helpful to identify problems unsolved so far, and to avoid unnecessary duplication of scientific work. The structure of the Supplement is the same as in the previous data compilation. However, some additional data characterizing protein-denaturant interaction and protein unfolding by trifluoroethanol have been added. In that context, some previous data have been reconsidered. The author wishes to thank everyone who provided data, ideas, or even unpublished results. Furthermore, support by the Deutsche Forschungsgemeinschaft (INK 16 BI-I) is gratefully acknowledged. Finally, I would like to thank the staff of Springer Verlag for their efforts and for excellent assistance during the production of the data collections.