Before initiation of antibiotic treatment, a specimen should be obtained for microbiological diagnostics. The first choice is an ulcer biopsy, as this method has the best microbiological diagnostic precision. It is important that the clinician arrives at the choice of diagnostics in consultation with the patient. On suspicion of an infection requiring deep revision, an ulcer biopsy should always be done. A chronically infected diabetic foot ulcer is infected with biofilm-forming bacteria. The biofilms are located in the ulcer and not on the ulcer surface, which means that they can only be ascertained by biopsies. The ulcer must be cleaned prior to sampling. This is done using the standard ulcer cleaning procedure, where necrotic tissue, pus and fibrin are removed, and the ulcer is rinsed with sterile saline or tap water. In connection with a biopsy, a tissue piece is removed after revision to vital tissue with a scalpel, biopsy forceps, biopsy stance or curette. The specimen is placed in a suitable container and must be transported to the department of microbiology as soon as possible. A little amount of sterile saline may be added if there is a risk of desiccation. The specimen is stored in a refrigerator until collection. If it is not possible to take an ulcer biopsy, a swab of the ulcer may be done instead using the Levine technique, as the ulcer swab sensitivity is clinically acceptable. An ulcer swab has a sensitivity of 88% in relation to identifying patients with disease-producing bacteria (pathogens) relative to an ulcer biopsy. On clinical suspicion of diabetic foot ulcer infection, it is essential that empirical antibiotic treatment be commenced without delay. It is important that the clinician does not wait for the test result or that the clinician does not postpone antibiotic treatment because no sample has been taken.