Diagnosans are members of a fictional alien race in the Farscape television series.
Due to their natural ability to detect and treat a variety of diseases in all types of living things, many of them become physicians. They have complex minds and an equally complex language, so much so that standard translator microbes cannot decode the intricacies of their speech. They are soft-spoken and gentle, further adding to their abilities as doctors. Diagnosans can diagnose disease in many different races, from humans to Leviathans, such as Moya.
Their primary flaw as a species is, ironically, their own inability to tolerate infection in their bodies. Typically, Diagnosans wear special masks whenever they are in a situation where they may come into contact with a contagion. Usually, they use a sterile force field when performing surgery, but they must put their mask back on before turning off the field, since even traces of a disease can prove fatal if inhaled into their nose and mouth.
In the episode, Die Me, Dichotomy, Grunchlk revealed he often froze the bodies of dying patients at the moment before death, in order to use their organs for other patients, and as such was able to find a compatible brain tissue sample for Crichton's operation. It is unknown if this cache of bodies was Grunchlk's design, or if all Diagnosans keep such organ reserves. The character Stark became extremely upset after realizing this, since he is a Stykera, and can communicate with dying individuals as they are crossing over. There is very little else that is known about Diagnosans, since they only appeared in a few episodes of Farscape.