Primary infection and reactivation of human cytomegalovirus (CMV) remain a major problem in immunocompromised patients, frequently resulting in a life threatening CMV disease. Intravenous polyvalent (hyper)-immunoglobulins (IVIG) can be administered for therapy and prophylaxis of CMV infections. However, only limited data about the efficacy and mechanism of action of IVIG products against viral infections in vitro are available so far. In this study, the effect of IVIG on CMV infection in vitro was investigated using isolates from CMV-infected patients as well as the laboratory strains AD169 and TB40. A qualitative and quantitative comparison of five different commercially available IVIG products in different human cell lines was performed concerning their ability (1) to neutralize cell-free virus, (2) to inhibit cell-to-cell spread and cell-associated transmission and (3) to influence CMV mRNA levels. All IVIG tested exhibited a high neutralization activity in epithelial and endothelial cell cultures (50% inhibition dose <0.1 mg/ml). However, qualitative differences between the products could be demonstrated in neutralization tests using human embryonal lung fibroblasts (HELF). The IVIG products also significantly differed in their ability to inhibit cell-to-cell spread within an CMV-infected HELF monolayer displaying inhibition rates that varied between 61 and 100%. No correlation between the ability to neutralize cell-free virus and to inhibit cell-to-cell spread could be observed. The incubation with IVIG influenced the amount of CMV immediate early and late mRNA, as indicated by a significant reduction in CMV mRNA in infected epithelial cells after incubation with IVIG in a dose-dependent manner. This study suggests different antiviral functions of polyvalent IVIG and confirms their potential to inhibit a CMV infection in vitro, with profound differences between the hereby used IVIG products.