INTRODUCTIONThis is the second of two protocols describing how to perform in situ hybridization on whole mouse embryos. Here we describe the hybridization procedure, and the localization of the DIG-labeled RNA using a conjugate of anti-DIG Fab antibody and calf intestinal alkaline phosphatase. Enzyme activity of the reporter is detected by a color reaction, resulting in the formation of a water-insoluble purple/blue precipitate.