This Special Report looks at three aspects of the search for ways to detect illicit substances such as illegal drugs and explosives. The first part examines how specialists are trying to improve the already striking ability of dogs to zero in on specific "odor signatures." The second part explores the wishes and wants of law enforcement and aviation security officials with regard to technology for detecting explosives. The third part describes a novel way of capturing the boundary layer of air that surrounds every human as a means of sampling for residues of illegal substances.