Luminol is a water-based solution capable of detecting blood that has been diluted up to 10,000 times. Once it comes in contact with blood, it reacts by causing the blood to fluoresce a pale blue color. This chemical has long been used by forensic investigators to search for and document imperceptible trace amounts of blood. However, few investigators have had much experience or training with luminol. There are associated health risks with luminol as it is a suspected carcinogen. Safety precautions are necessary to assure safety and limit exposure. The luminol solution can be prepared in the field, but it is recommended that it be mixed in a lab under controlled conditions. In addition, because it can give false positive reactions, it is only a presumptive positive test for blood. Once areas are identified for luminol treatment the scene must be prepared, which requires the environment where it is used to be as dark as possible. The camera, for photographs, must be set up and ready to document any reaction that is observed with the recommended use of a 35mm single lens reflex camera with manual settings. Training is imperative when using luminol. It is necessary for investigators to have a comfort level with the safety procedures, personal protective equipment, and techniques of luminol application and documentation before they attempt it on evidence. Practice with luminol is recommended in a controlled environment. Photography techniques can be practiced in a dark room or an interior room with no lights. Luminol can help detect evidence that may never be found by just an investigator’s eyes. When used safely and appropriately, luminol is a great investigative tool.