IN connexion with some recent legal proceedings, a new method for detecting fingerprints has been discovered by one of us (S. O.). The method involves the well-known ninhydrin test for amino-acids, often used in chromatography. In this method, fingerprints on paper have always been considered a great nuisance, and one is often recommended to use forceps “to avoid fingerprints”1. In our opinion, the new method will be most suitable for detecting fingerprints on paper and similar materials. Some of the results have a wider interest, and a brief report on the new application of ninhydrin is therefore presented.