Infectious diseases and cancer change a patient's metabolism and hence the metabolic compounds produced. The composition of volatile organic compounds (VOCs) in exhaled breath or urine or stool samples can therefore be characteristic of a particular disease. In recent years many studies have been conducted into the training of animals, including dogs, to recognise diseases by smell. Besides trained animals, electronic noses (e-noses) are also being developed. These devices can identify disease-specific odour profiles in VOCs. Although the results of research in the field of scent diagnosis are promising, the medical community remains largely sceptical. We discuss applications of scent detection as a diagnostic tool in modern medicine.