Ninhydrin derives bearing alkylthio substituents at position 5 were prepared from their corresponding 6-thionindanones by oxidation with N-bromosuccinimide and dimethylsulfoxide. Absorption spectra in solution were recorded on an ultraviolet spectrophotometer, and two light sources were used for luminescence excitation. Latent fingerprint samples of various individuals were collected on four types of paper items: groundwood-free white paper, checks, Israeli bank notes, and $1 U.S. bills. It was found that all 5-thioninhydrins reacted with alanine to give colored products. All developed latent fingerprints on paper to give images similar to those obtained with ninhydrin. Their sensitivity markedly exceed that of ninhydrin and even that of 5-methoxy ninhydrin. Alkylthio ninhydrins, as fluorogenic fingerprint reagents, were characterized by the following properties: both colored and fluorescent images, intense fluorescent images, wide range of excitation, minimal background discoloration, convenient application, and enhanced fluorescence upon cooling to liquid nitrogen temperature. 15 references, 1 table, and 3 figures (Author abstract modified)