Sarcoidosis is a multisystem granulomatous disorder of unknown etiology, most commonly affecting young adults presenting most frequently with bilateral hilar lymphadenopathy, pulmonary infiltrations, skin or eye lesions (1). Borrelia burgdorferi, the causal agent of Lyme disease, could also be responsible for sarcoidosis. Domestic animals may play a major role in transmitting the disease to humans. The modes of transmission to such animals and possible contact transmission to humans are still obscure and should be more fully investigated. Small rodents have been found to play a role as reservoirs for Borrelia burgdorferi. They are suspected to constitute an important source of contamination for domestic animals. The author explains in this paper how geographic distribution and familial occurrence of sarcoidosis as well as racial differences in the incidence of this disease, could be related to such findings.