Mycoplasmas are the smallest known free-living organisms, and adapted to a special mode of life as commensal organisms or opportunistic pathogens. Because of their small genome size, they have limited biosynthetic capacity, which means they lack many biochemical pathways found in the Eubacteria. They are highly adapted to their host, which provides most of its nutritional requirements for growth. For this reason, there are only a few biochemical properties that can be investigated in the diagnostic laboratory. Consequently, identification of mycoplasmas is greatly reliant on serological tests based on the recognition of structural membrane proteins by specific antiserum. However, preliminary biochemical characterization can reduce the battery of sera required for final serological identification.