Magnetic resonance imaging (MRI) of the brain was performed on forty-five patients with multiple sclerosis (MS), using T1-weighted inversion recovery and T2-weighted spin echo images, and the results were compared with X-ray computed tomography (CT). Some of the 45 MS patients were also examined by neurophysiological studies (visual evoked potentials and auditory brainstem responses) to compare with the brain MRI findings. MRI showed demyelinating plaques of the brain in 20 (74%) of 27 patients with brain symptoms, 11 (61%) of 18 patients without symptoms and 31 (69%) of all 45 patients. In 27 patients with brain symptoms, MRI was able to detect brain lesions in 6 (86%) of 7 acute stage patients and 14 (70%) of 20 non-acute stage patients. Furthermore, MRI was able to detect brain lesions in 21 (70%) of 30 clinically definite MS patients and 10 (67%) of 15 clinically probable MS patients. X-ray CT was performed on all 45 patients and was able to detect brain lesions in 9 (33%) of 27 patients with brain symptoms and 1 (6%) of 18 patients without symptoms. Visual evoked potentials were evaluated in 31 patients, and showed abnormalities in 1 (11%) of 9 patients without symptoms of optic neuritis and 100% of 22 patients with symptoms. Auditory brainstem responses were evaluated in 19 patients, and showed abnormalities in 1 (11%) of 9 patients without brainstem symptoms and 3 (30%) of 10 patients with symptoms. MRI of the brain was markedly superior to X-ray CT, visual evoked potentials and auditory brainstem responses in detecting clinically unsuspected lesions.(ABSTRACT TRUNCATED AT 250 WORDS)