We have developed a sensitive, ELISA-based assay to detect autoantibodies to myelin basic protein (MBP) in human serum. Autoantibody levels were measured in 98 normal healthy adults (age range 20-66) and 94 clinically definite multiple sclerosis (MS) cases (age range 18-63). Of the MS patients, 77% had elevated levels of MBP autoantibodies (IgG) whereas only five normal individuals had antibody levels increased over normal. From the receiver-operator curve (ROC), the mean+/-2SD as clinical decision limit offers high sensitivity (77%) and specificity (95%). No change in assay performance was observed when hemoglobin, triglycerides or bilirubin were added to serum samples. The success of the assay is dependent on the use of heparin, an anionic molecule, which neutralizes the positive charge on the highly cationic MBP.