Researchers have long reported that dogs and cats improve the physical and psychological health of their human caregivers, and while it is still inconclusive, a substantial amount of research now lends support for the commonly held view that pets are good for us. Recently, studies have directed attention toward exploring the use of animals, most notably dogs, in the detection of disease and other types of health problems in people. This article reviews the evidence for dogs' ability to detect ill health in humans, focusing specifically on the detection of cancer, epileptic seizures, and hypoglycemia. The author describes the research carried out in this area and evaluates it in an effort to determine whether dogs have a role to play in modern health care as an alert tool or screening system for ill health. Where necessary, the author has highlighted weaknesses in the work and proposed directions for future studies.