No exact information exists on the diagnostic value of immunohistochemistry applied to the routine material of an institute of surgical pathology. For this reason 390 cases additionally investigated by immunohistochemistry were analyzed retrospectively. This method was applied to 0.5% of all biopsies studied morphologically. On average 4.4 antisera per case were used. 352 cases (90.3%) initially diagnosed by morphology alone (16 benign lesions of debatable type, 111 lesions not clearly defined as benign or malignant, 225 malignant tumours of unknown subtype) could be clarified by immunohistochemistry. To obtain reliable results specific application of immunohistology and a clearcut formulation of the question are necessary. If these criteria are fulfilled immunohistochemistry represents a powerful tool in surgical pathology.