Eperythrozoonosis of swine (also designated as porcine mycoplasmosis) is a disease of swine under stress, expressed as a febrile condition with development of an acute ictero-anemia. It is caused by Eperythrozoon suis and usually causes a subclinical infection with a latent carrier state that persists for extended periods. In China, this disease has gradually developed as an important intercurrent disease and an emerging swine disease that, in recent years, has spread throughout all provinces except Tibet. Classical swine fever (hog cholera), porcine influenza, swine enzootic pneumonia, porcine reproductive and respiratory syndrome (blue ear disease), streptococci, and toxoplasmosis were detected in Eperythrozoonosis-infected pig herds, and caused serious economic losses. National epidemiology surveillance in 2002 revealed that this disease caused a total morbidity of 30% and a mortality of 10-20%. Total mortality (which includes culling sick pigs) was more than 60%. The morbidity within infected herds was near 100%, has spread throughout with a total mortality rate usually over 50%. Mortality of piglets in some districts was as high as 50%. The highest infection rate on pig farms was more than 90%. The farms with higher infection rates occurred in pig-raising areas during epidemic seasons. New diagnostic tests, such as ELISA and PCR, have been developed for the detection of porcine eperythrozoonosis, but traditionally the diagnosis of the disease is still based on clinical history and optical microscopic examination of the causative agent in blood smears. Efficient preventive and control measures include the detection of carriers in pig herds and treatment of sick pigs with drugs, such as long-acting oxytetracycline, doxycycline, or aceturate of diminazene. Oxytetracyclines as feed additives have been introduced for eperythrozoonosis prevention in uninfected pig herds, and pig producers have taken measures to reduce stress and improve sanitary conditions.