On the basis of the results of a collaborative study the Expert Committee on Biological Standardisation of the World Health Organisation has issued an international standard (IS) serum for parvovirus B19 IgG antibody (NIBSC 93/724). In this study this IS was used to calibrate an in-house standard serum for reporting the results of parvovirus B19 IgG testing in IU/ml. The IgG titre distribution in 939 pregnant women was determined. These samples were sent to the laboratory for determining the immune status to parvovirus B19 following contact with parvovirus B19 infected individuals or for detecting acute infection in patients with symptoms suggestive of parvovirus B19 infection.