101 patients with multiple sclerosis (MS) (53 definite, 22 probable, 8 possible and 18 suspected according to the McDonald and Halliday criteria) were investigated by magnetic resonance imaging (MRI), to evaluate its diagnostic sensitivity compared to other diagnostic parameters such as cerebrospinal fluid (CSF) findings and auditory brainstem responses (ABR). In addition, correlations between severity of lesions on MRI and clinical data (disability duration of the disease and progression rate) and CSF immunoglobulin abnormalities were evaluated. MRI detected multiple demyelinating lesions in 96% of definite, 77% of probable, 50% of possible and 56% of suspected MS. In the same groups CSF was positive for oligoclonal banding in 85%, 68%, 50% and 37% and ABR in 82%, 50%, 80% and 28% respectively. Severity of MRI was found to correlate with disability and duration of the disease, but not with progression rate. The presence of CSF oligoclonal bands and a raised and IgG index were usually associated with more extensive white matter involvement as evaluated by MRI.