35 intracranial tumours, 18 gliomas, 12 meningiomas, one neurilemmoma (neurinoma), one malignant melanoma and two metastases were successfully grown in-vitro and were submitted to immunocytochemical reactions, including cytokeratin, glial fibrillary acid protein (GFAP), vimentin, fibronectin, S-100 protein, neurofilament proteins, neuron-specific enolase (NSE) and basic myelin protein (MBP). Cytokeratin in metastases, GFAP and vimentin in gliomas, vimentin in meningiomas were consistently positive. S-100 protein was weakly and partially positive in gliomas, meningiomas, the neurilemmoma and malignant melanoma. Positive demonstration of fibronectin within cells was interpreted as a consequence of phagocytosis, except in meningiomas where fibronectin expression next to cell membranes seemed genuine. All other tested markers proved negative. The most important result seems to be that cells expressed markers irrespective of cellular shape and cytological morphology. It can be concluded that the cellular population as a whole consisted of tumour cells during the short time under observation and that supportive cell contamination during this early growth period was negligible.