1. The diagnosis of a parasitic infection by allowing a noninfected disease-carrying organism; such as, a mosquito to feed on an infected person's blood and then examining the organism for infection.
2. Diagnosis of an infectious disease at an early stage by exposing a presumably infected individual or tissue to a clean, laboratory-bred mosquito, tick, or other vector, and then examining the vector for the presence of the infective microorganism.

The diagnosis or the diagnostic system used to find out the existence of an infectious disease of a microorganism: By the use of xenodiagnosis, an infected area is exposed to a vector animal host, and afterwards the infected host is examined for the pathogen.