Because of their superior olfactory sense, trained dogs are often used in the investigation of crimes. This study compared the sensitivity of two dogs versus three common blood presumptive tests (luminol, tetrabase, and Kastle-Meyer). The results revealed that the surface area that contained the blood contamination was an important factor. A smooth, nonporous surface (vinyl) was more difficult for dogs; some blood presumptive tests outperformed dogs on this surface. However, on a rough, porous surface (carpet), the dogs were superior. The findings cannot be directly extrapolated to field situations, but can be used in support of training dogs to enhance their sensitivity and to improve the application of blood presumptive tests. (Published Abstract)