A definitive diagnosis is crucial for management of any oral mucosal disease. Direct immunofluorescence (DIF) is a valuable diagnostic aid for immune-mediated blistering diseases and systemic connective tissue diseases of the skin and the mucosa. This paper gives an overview of the DIF biopsy technique for oral lesions and provides a background for the clinician to optimize the utilization of DIF biopsy. The key characteristic diagnostic findings of DIF of specific mucosal diseases are also discussed. Schlagwörter: direct immunofluorescence, immune-mediated blistering diseases, oral vesiculobullous disease, oral biopsy technique, systemic connective tissue diseases