To assess whether TGF-beta isoforms are significantly increased after intravenous immunoglobulin (i.v.IG) infusion in the plasma of patients with multiple sclerosis (MS), 19 patients with clinically definite MS were enrolled in a double blind placebo controlled i.v.IG study. TGF-beta1, TGF-beta2, TGF-beta3 plasma concentrations were measured prior and directly after i.v.IG infusions by specific ELISA. Compared to the placebo group, we found a significant increase in the plasma levels of all three TGF-beta isoforms in patients treated with i.v.IG. The significantly increased TGF-beta plasma concentrations in treated patients suggest an additional, immediate mechanism of action that may accompany the molecular effects of i.v.IG therapy in MS. The variable amount of the potent anti-inflammatory TGF-beta isoforms within the i.v.IG preparations may exert a differentiated view regarding the manifold indications of i.v.IG therapy.