Previous studies have demonstrated that maturation of cytomegalovirus (CMV)-specific antibodies in solid organ transplant recipients is delayed after primary CMV infection. To investigate the clinical significance of this finding, the avidity indices of anti-CMV antibody were determined in parallel with other serologic and virologic parameters in serial serum samples from 24 solid organ transplant recipients who had primary CMV infection that began during the first 3 months after transplantation. The data obtained show that a delay in antibody maturation is significantly correlated with a long persistence of positive antigenemia.