Spirochetes could be cultivated from 9 out of 13 skin biopsies from patients with erythema chronicum migrans Afzelius (ECMA) and from 2 out of 5 biopsies from patients with acrodermatitis chronica atrophicans (ACA) by using a newly modified serumless Kelly's medium. The different spirochete strains grew best at a low oxygen tension. Attempts to grow spirochetes from blood and cerebrospinal fluid failed. The cultivation of spirochetes from secondary ECMA lesions favours the presumption that a spirochetemia may occur in ECMA. The isolation of spirochetes from an ACA patient who had a disease duration of greater than 10 years proves that the spirochetes may survive in the human body for a considerable time.