A commercial Epstein-Barr virus (EBV) antivirus capsid antigen (VCA) IgG antibody ELISA and an 'in-house' EBV VCA IgG immunofluorescence antibody assay (IFA) were used to detect EBV VCA IgG antibodies in 100 serum samples collected from organ transplant recipients and immunocompetent individuals. The avidity of EBV VCA IgG antibodies was determined in the IFA and ELISA using the mild reducing agent 8 M urea to remove low avidity antibodies. The samples were collected from patients who had previously been identified with a primary EBV infection, a reactivation of latent infection or evidence of a past EBV infection by means of EBV-specific serology. Using the ELISA, the antibody avidity was low in samples collected from patients with recent EBV infection and high in samples collected from patients with a past infection or a reactivation. There was a statistically significant difference of means (P < 0.001) of percentage reduction in optical density values, measured in the presence of 8 M urea, obtained with samples collected from patients with recent infection compared with samples from patients with a past infection or a reactivation of latent infection.