In a first experiment we tested different samples of the HOCl-modified HSA, which were generated by using different HOCl concentrations, in a syncytium inhibition assay. In HIV-1 cell cultures, infected cells fuse with other, non-infected CD4 + target cells. Cell-cell fusion is known as syncytium formation. Syncytium formation is the result of the binding of gp120, which is present on membranes of the infected cells, to the receptors on the target cells and subsequent insertion of the gp41 N-terminus into the host membrane. This gp120-receptor binding event promotes recurring cell-cell fusion which leads to the generation of large syncytia. The mHSA samples generated with low HOCl concentrations (molar ratios HSA:HOCl 1:10 and 1:50) showed no inhibitory effect on syncytium formation (Figure 1 ). At higher concentrations (molar ratio 1:100) an inhibitory effect of mHSA was detected with 90% inhibition at a concentration of approximately 50 μg/ml. The mHSA samples produced at molar ratios 1:1000 and 1:10.000 showed strong inhibition with 90% at 10 μg/ml and complete inhibition of gp120-induced syncytium induction at 20 μg/ml. Thus, HSA treated with higher concentrations of HOCl is transformed into an antiviral form in contrast to HSA samples treated with low HOCl doses.