The enzyme beta-galactosidase was first mentioned in the literature by Beijerinck exactly a hundred years ago. The Department of Microbiology and Enzymology of the Delft University of Technology keeps the memory of Beijerinck, its first professor, alive by maintaining a 'Beijerinck-room' in the attic of the building. In addition to manuscripts and laboratory notebooks, this room contains some of his chemicals and biological preparations, and it was here that we recently found a 90-year old lactase preparation. Even after storage under suboptimal conditions, the preparation still exhibited measurable enzyme activities.