The binding specificity of the murine OKT3 has been transferred into a human antibody framework in order to reduce its immunogenicity. “Humanized” anti-CD3 mAbs, such as gOKT3-5 and gOKT3-7, have been shown to retain, in vitro, all the properties of native OKT3, including T cell activation which has been correlated, in vivo, with the severe side-effects observed in transplant recipients after the first administration of the mAb. Disclosed are modified versions of humanized anti-CD3 mAbs that do not have the property of T cell activation. Further dislosed are methods of using such mAbs.