The present clinical observation is related to a 14-year-old girl suffering from acute myeloid leukemia. The clinical course was complicated by episodes of severe enterocolitis, E. coli- septicemia, pancreatitis and pneumonia. In the course of continued cytostatic and antibiotic treatment a persistent asymptomatic Lactobacillus casei subsp. rhamnosus-bacteremia became detectable by a total of 18 blood cultures. Microbial cultures of the faeces revealed colony-forming unites of this germ in orders of 10(9)/g. Antibiotic eradication attempts according to the resistogram were not successful. The Lactobacillus-bacteremia disappeared only after 13 months when the cytostatic therapy was terminated. An adjuvant influence of the Lactobacillus infection on the outcome of the underlying disease cannot be excluded.