The imaging findings of brain-stem lesions are often nonspecific and histological diagnosis is limited because of fear of complications associated with biopsy. A noninvasive method for tissue characterization is therefore highly desirable. We undertook a review of proton magnetic resonance spectroscopy (MRS) of patients with solitary brain-stem lesions to determine if MRS could characterize them. We carried out single- or multivoxel proton MRS using long echo times (135 or 270 ms) on 34 patients with solitary brain-stem lesions. We analyzed the following peaks: choline (Cho), creatine (Cr), N-acetylaspartate (NAA), and lipids/lactate (Lip) and calculated peak height ratios for Cho/Cr, NAA/Cr and Lip/Cr. The results were compared with histology in nine patients and with the presumptive diagnosis in 25. We also performed single-voxel proton MRS on the brain stem of five normal volunteers. There were differences in all ratios between controls and the patients with neoplastic and non-neoplastic lesions: Cho/Cr was low in non-neoplastic and high in neoplastic lesions (control: 1.8+/-0.1; non-neoplastic: 1.4+/-0.2; neoplastic: 2.0+/-0.2); NAA/Cr was low in non-neoplastic, and lower in neoplastic lesions (control: 2.3+/-0.1; non-neoplastic: 1.4+/-0.2; neoplastic: 1.2+/-0.1), and Lip/Cr was elevated in both neoplastic and non-neoplastic lesions (control: 0.04+/-0.02; nonneoplastic: 1.9+/-0.7; neoplastic:1.9+/-0.7).