It is reported on 2 cases of Klebsiella-septikaemia with difficult course. Germs of the group Klebsiella aerogenes could be proved microbiologically. On the basis of the peculiarities of the clinical course the author adopts a definite attitude to the development of the infection, the pathogenesis, to the microbiological proof and to the aimed antimicrobial chemotherapy. The antibiotic treatment was successful in the first case with karbenicillin and gentamycin and in the second case with cephalotin and gentamycin during 4 weeks when a penicillin allergy was present and following this with chloramphenicol and streptomycin during 3 weeks.