We read with great interest the article by Sonoda et al 1 on canine scent detection in those with colorectal cancer. The concept of using a dog to detect diseases is not new; there are many reported incidents of dogs barking at their owners (or even trying to bite the leg off of an owner with melanoma!) who are later shown to have the disease. Several studies have shown that dogs are able to detect, among others, breath, lung, bladder, ovary, prostate and skin cancers. In these reports, the dog is trained to recognise the disease state (in fact, the dog is reminded of these different groups …