Seventy-four consecutive pediatric liver transplant recipients were reviewed to assess the effect of the monoclonal anti-T-lymphocyte antibody OKT3 on subsequent viral infection (9 patients were excluded due to postoperative demise during the 1st week). Twenty-two patients received OKT3 in addition to standard cyclosporine-prednisone immunosuppression for either steroid-resistant acute rejection (18) or to facilitate reduction of cyclosporine due to severe renal impairment (4). Invasive infections were diagnosed by histology or culture in tissue biopsies or bronchoalveolar lavage specimens. The overall incidence of viral infection was 58%, half of which was due to cytomegalovirus (CMV). Invasive viral disease was associated with increased mortality (37% vs. 3% p = 0.001). Viral-related deaths were due to CMV (5), disseminated adenovirus (3), disseminated enterovirus (1) and respiratory syncytial viral pneumonia (1). The use of OKT3 was associated with increased viral disease (59% vs. 33% p=0.04) and invasive primary CMV disease (58% vs. 19% p=0.04). Trends were observed toward increased overall viral infection (73% vs. 51 % p=0.08), primary CMV infection (58% vs. 25% p=0.08) and overall mortality (27% vs. 9% p =0.08) following OKT3 therapy. We conclude that pediatric liver transplant recipients who require OKT3 therapy may be at increased risk for invasive viral disease and especially invasive primary CMV disease.