We have assessed the diagnostic value of the determination of cerebrospinal fluid lactate dehydrogenase, carcinoembryonic antigen, beta 2-microglobulin, beta-glucuronidase and total protein, using linear discriminant analysis, in detecting central nervous system metastases from extracranial malignancies. We conclude that, using these tests, it is impossible to differentiate between control individuals and patients with brain or epidural metastases. Leptomeningeal dissemination from either solid tumours or non-Hodgkin lymphoma could be differentiated from control individuals and patients with brain or epidural metastases. In this differentiation it is essential that bacterial, fungal or tuberculous meningitis be excluded from the differential diagnosis by other diagnostic procedures. The combination of beta-glucuronidase and beta 2-microglobulin provides almost the same diagnostic information as the combination of all parameters.