This article describes the value of laboratory diagnostic procedures in the diagnostic arsenal of otolaryngologists. The rational and therefore the rationale of the application of laboratory medical methods are critically evaluated. In the era of diagnosis-related groups a high value is placed on a rational laboratory diagnostic, in the sense of a cost-oriented medicine, so that the laboratory diagnostic procedure is always carried out in stages, just as in other diagnostic procedures. The possibilities of clinical chemistry, separated into the theme blocks "clinical chemical basic diagnostics", "haematological parameters", "coagulation investigations" and "immunological diagnostics" are demonstrated based on examples. These are aimed at the needs of otolaryngologists, in that the emphasis in each theme block is centred on the indications and evaluation of the individual laboratory investigation.