An antibody binding to IGF-IR and inhibiting the binding of IGF-I and IGF-11 to IGF-IR which is characterized in that said antibody is a) is of IgGI isotype, b) shows a ratio of IC 50 values of inhibition of the binding of IGF-I to IGF-IR to the inhibition of binding of IGF-II to IGF-IR of 1:3 to 3:1,c) inhibits for at least 80% at a concentration of 5 nM IGF-IR phosphorylation in a cellular phosphorylation assay using 3T3 cells providing 400,000 to 600,000 molecules IGF-IR per cell in a medium containing 0.5% heat inactivated fetal calf serum (FCS) when compared to such an assay without said antibody, andd) shows no IGF-IR stimulating activity measured as IGF-IR phosphorylation at a concentration of 10 µM in a cellular phosphorylation assay using 3T3 cells providing 400,000 to 600,000 molecules IGF-IR per cell in a medium containing 0.5% heat inactivated fetal calf serum (FCS) when compared to such an assay without said antibody has improved properties in antitumor therapy.
