BACKGROUND: The signal of choline containing compounds (Cho) in proton magnetic resonance spectroscopy (1H-MRS) is elevated in brain tumors. [11C]choline uptake as assessed using positron emission tomography (PET) has also been suggested to be higher in brain tumors than in the normal brain. We examined whether quantitative analysis of choline accumulation and content using these two novel techniques would be helpful in non-invasive, preoperative evaluation of suspected brain tumors and tumor malignancy grade. METHODS: 12 patients with suspected brain tumor were studied using [11C]choline PET, gadolinium enhanced 3-D magnetic resonance imaging and 1H-MRS prior to diagnostic biopsy or resection. Eleven normal subjects served as control subjects for 1H-MRS. RESULTS: The concentrations of Cho and myoinositol (mI) were higher and the concentration of N-acetyl signal/group (NA) lower in brain tumors than in the corresponding regions of the normal brain. There were no significant differences in metabolite concentrations between low- and high-grade gliomas. In non-tumorous lesions Cho concentrations were lower and NA concentrations higher than in any of the gliomas. Enormously increased lipid peak differentiated lymphomas from all other lesions. The uptake of [11C]choline at PET did not differ between low- and high-grade gliomas. The association between Cho concentration determined in 1H-MRS and [11C]choline uptake measured with PET was not significant. CONCLUSION: Both 1H-MRS and [11C]choline PET can be used to estimate proliferative activity of human brain tumors. These methods seem to be helpful in differential diagnosis between lymphomas, non-tumorous lesions and gliomas but are not superior to histopathological methods in estimation of tumor malignancy grade.