In vivo sodium-23 magnetic resonance (MR) imaging in the head was performed in ten normal volunteers and six patients with brain tumors on a commercially available 1.5 Tesla whole-body MR system. Although sodium MR signal from the brain parenchyma could hardly be detected on routine spin echo (SE) pulse sequence, free induction decay (FID) image with echo time of 1.9 msec demonstrated MR signal in the normal brain tissue. On the other hand, extracellular sodium of cerebrospinal fluid, large venous sinus, and vitreous humor offered high sodium MR signal intensity due to the quantity of sodium and the relatively longer transverse relaxation time (50-60 msec) compared to that of intracellular sodium (less than a few msec). Strong signal was obtained in gliomas with superior contrast, though the delineation of the tumor tissue from edema was as difficult as when seen on proton T2 weighted SE image. Meningioma itself gave much less of a sodium MR signal compared to glioma. Peritumoral edema associated with meningioma showed a markedly high sodium MR signal which was more prominent adjacent to the tumor, although proton SE image revealed the peritumoral edema as homogeneous. Pathological tissues such as brain tumors and edema could be readily depicted as significantly high sodium-23 MR signal, apparently different from normal brain tissues. The current status of in vivo sodium MR imaging is discussed. The authors concluded that early clinical experience of in vivo sodium-23 MR imaging brought promising results in the evaluation of brain tumors and edema; otherwise, discrimination and quantification of multiple T2 components and the improvement of spatial resolution are desperately needed.(ABSTRACT TRUNCATED AT 250 WORDS)