Protocol describes here a high sensitivity indirect detection procedure for DIG-labeled hybridization probes. The procedure uses the components of the HNPP Fluorescent Detection Set to form a fluorescent precipitate of HNPP (2-hydroxy-3-naphthoic acid-2’-phenylanilide phosphate) and Fast Red TR at the site of hybridization. Includes: In situ hybridization with DIG-labeled probes; Detection of DIG-labeled probes; Fluorescence microscopy.