The intracytoplasmatic glycolytic enzyme neuron-specific enolase (NSE) can be found in cells of endocrine tissue and their derived tumours. The enzyme is not secreted but released if cells are destroyed, i.e. continuously in malignant tumours. The serum level of neuron-specific enolase (NSE) has been used as a marker for small cell carcinomas of the lung, glioblastomas and malignant phaeochromocytomas. In this investigation blood samples were taken prior to and following surgical manipulation of the tumour in 21 patients with paragangliomas of the head and neck region and 6 controls. 22 serum samples were obtained before angiography and two hours after angiography, 41 before surgery, during surgery and after surgery. The serum level of NSE was measured by NSE-RIA test (Diagnostics, Uppsala). In all tumour specimens NSE could be demonstrated by the immunohistological PAP method (Abb. 1). Only two patients had preoperatively elevated serum-NSE levels. An arterial venous shunt had been detected by angiography in one of these patients. No significant effect on NSE serum level could be produced in the majority of patients by an angiography with embolisation or surgical manipulation of the tumour (Fig. 1, 2). A reduction in serum NSE level was observed postoperatively in both cases mentioned before. None of the 6 controls showed any significant change in serum NSE level (Fig. 3). It can be concluded from this study that embolisation does not lead to direct or indirect cell destruction through ischaemia. Manipulation of the tumour does not destroy a significant number of cells.(ABSTRACT TRUNCATED AT 250 WORDS)