Fourteen patients with cerebral gliomas were studied with positron emission tomography (PET) using L-[methyl-11C]methionine (11C-MET). Positive images of tumour were obtained in all cases regardless of histological grades. The analysis of differential absorption ratio (DAR) showed the higher accumulation of 11C-MET in high grade gliomas than in low grade gliomas. PET study with 11C-MET will be of great value not only in delineating the location of gliomas, but also in making a qualitative diagnosis from the view point of the biological properties of gliomas.