BACKGROUND AND OBJECTIVES: Although parvovirus B19 is a significant blood product contaminant, few methods other than polymerase chain reaction (PCR) have been developed to detect the presence of the virus. MATERIAL AND METHODS: A B19 antigen enzyme immunoassay (EIA) has been developed and the sensitivity of detection is ascertained using dilutions of the B19 capsid protein VP2 and 10-fold dilutions of B19 viraemic serum. Once the assay cut-off was established, a panel of viraemic donations (n = 70) was screened by the antigen EIA. The B19 immunoglobulin M (IgM) and IgG status of these specimens was also determined. During screening of blood donor units by quantitative PCR, 70 individuals were identified with levels of B19 DNA greater than 10(6) IU/ml at the time of blood donation. RESULTS: The sensitivity of the B19 antigen EIA was estimated to be equivalent to between 10(8) and 10(9) IU/ml B19 DNA or 1-10 pg/ml of recombinant capsid protein. B19 detection was significantly enhanced when viraemic specimens were pretreated with a low pH proprietary reagent. Unlike other virus-detection assays, detection of the B19 antigen was not affected by the presence of B19 IgM or IgG antibodies. In addition, the assay was capable of detecting all three genotypes of human erythrovirus. Combined specimen analysis by the B19 antigen assay and a B19 IgM assay facilitated the detection of 91% of acute B19 infections in the test population. CONCLUSION: In combination with B19 IgM detection, application of the B19 antigen EIA is a flexible and efficient method of detecting recent B19 infection and can be used as an alternative to PCR.