Using radioimmunoassay we measured serum levels of insulin-like growth factor (IGF)-1 and IGF binding protein (IGFBP)-3 in patients with relapsing multiple sclerosis (MS) and a benign course (Expanded Disability Status Scale (EDSS) < or =3 despite > 10 years disease duration), relapsing MS with cumulative disability leading to an EDSS score >4 within 10 years of disease duration, primary progressive MS and healthy controls. We found no differences in IGF-1 and IGFBP-3 serum levels, and the IGF-1/IGFBP-3 ratio between the four groups. However, there was a significant correlation (P =0.005) between IGFBP-3 serum levels and both the progression index of disability and the Multiple Sclerosis Severity Score in patients with primary progressive MS.