the most amazing thing i saw, was on a crime show. a dog had been taught to recognise human blood, and distinguish it from other blood. they caught the murderer, and in court they took the dog in and placed three bags, 2 with blood soaked cloth in them and another one with a teeny spot of blood. the 2 blood soaked cloth was covered in cows and pigs blood (or similar animals, cant really remember) and the teeny spot of blood was human blood, and the dog still managed to smell it and indicted on the correct bag! it was amazing to see

I saw a programme on sniffer dogs used in the port of Los Angeles where one of them who was trained to pick up on explosives indicated that he had found something. The authorities evacuated the whole port and this place is huge, we are talking several thousand people, not to mention a queue of ships waiting to get in and out within a very narrow window in the tide.

Once the port was clear they put the suspect suitcase through an x-ray machine and saw what looked to be a hand grenade, but whilst waiting for the bomb squad they were also able to locate the owner of the case who was able to quickly put their minds at rest. The hand grenade shape was in fact a piece of coral the man had brought back from a diving holiday, but that still didn't explain why the dog had gone for the case.

It turns out that the guy had used the same case to transport a handgun and ammunition to his gun club, six months ago, and the dog still picked up traces of the ammo, after 6 months! That's a pretty powerful nose!

I have also read about assistance dogs that can pick up the scent released just prior to an epileptic fit and warn their companion to put themselves in a safe position, apparently in cases extreme enough to warrant the use of such a dog, it is a regular life saver. But the single most amazing one has to be dogs that can detect cancer in a patient before it shows up on a scan, that really blew me away.