The formation of the disulfide bond in peptide HVEM(23–39) was performed after purification. The peptide was dissolved in a mixture of H2O and methanol (1:9, v:v), the final volume was 1.5 l and the concentration of the peptide was established at 40 mg/l. The pH was adjusted and kept between 8 and 9 by using ammonia whilst stirring the solution at room temperature for 3 days in the presence of atmospheric oxygen. Reaction progress was monitored by analytical RP-HPLC in a gradient of 5% to 100% B in A in 60 min. When the reaction of oxidation was completed the solvents were evaporated and the peptide was lyophilized.