Beta 2-microglobulin (beta 2-MG) levels were determined in serum, cerebrospinal fluid (CSF), and tumor cyst fluid obtained from patients with a variety of intracranial tumors. In addition, a simultaneous determination of the carcinoembryonic antigen (CEA) was carried out in some patients. The beta 2-MG levels were elevated in 11/101 intracranial tumors, including glioma (4/34), non-glial tumors (1/18), malignant lymphoma (2/18), and metastatic brain tumors (4/31). There were no significant differences in the beta 2-MG levels of serum among the different patient groups. On the other hand, the beta 2-MG levels in CSF were significantly higher in patients with malignant lymphoma and metastatic brain tumors than in those with glioma and non-glial tumors. Fifteen (83.3%) of 18 patients with malignant lymphoma and 6(25.0%) of 24 patients with metastatic brain tumors showed increased the levels of beta 2-MG in CSF. The beta 2-MG levels in the tumor cyst fluid of 11 intracranial tumors exceeded normal serum levels in all but two patients. When the CEA levels in the serum and CSF were measured simultaneously, meaningful differences between malignant lymphoma and metastatic brain tumors were clearly observed. The highest incidence and highest levels of the CEA in serum and CSF were only noted in patients with metastatic brain tumors. Conversely, the serum CEA was slightly raised in 11.8% of malignant lymphoma and the levels of CEA in CSF were within normal range in all these patients. Serial determination of CSF beta 2-MG in patients with malignant lymphoma correlated well with their clinical findings.(ABSTRACT TRUNCATED AT 250 WORDS)