W. Siegenthaler's and G. Siegenthaler-Zuber's opinion, according to which in the majority of infections in practice an etiological (microbiological) diagnosis may be renounced and the guiding slogan "before therapy the gods have placed the diagnosis" should be relativized for the situation in the practice in contrast to the situation in the clinic, is opposed. Microbiological findings represent an unrenouncable basis for a rational antimicrobial chemotherapy in practice and clinic. In the individual case this does not exclude a calculated chemotherapy on account of a clinical and microbiological tentative diagnosis made by the physician in charge. But at the latest when the empiric therapy fails an efficient microbiologic diagnostics must be at our disposal.