Serum markers, e.show $132#g., the protein S-100B and neuron-specific enolase (NSE), are recognized to give additional information about the extension and prognosis of brain damage. In some of these patients it is necessary to insert a ventricular drain. Whether the cannulation of the ventricle falsifies the serum concentrations of these markers is unknown. The aim of this study was to get further information in this field. In this prospective study we included 19 patients. All patients underwent ventricular tapping and insertion of a ventricular drain. Serum samples for estimation of S-100B and NSE were collected before, directly after and 6 h after insertion. In addition we investigated the cerebrospinal fluid (CSF) directly after and 6 h after insertion. All patients but one showed no significantly increased S-100B or NSE serum concentration after insertion of the drainage. The concentrations in the CSF were significantly higher. One patient showed increasing concentrations of the markers in all samples reflecting ongoing brain damage. The serum values of S-100B and NSE seem not to be falsified by insertion of a ventricular drain. Therefore the prognostic value of these serum markers seems to be preserved despite the surgical manipulation.