The authors investigated the incidence of pulmonary complications following immunosuppression with monoclonal antibodies (OKT3) in a series of 100 consecutive cases of orthotopic liver transplantation (OLT). Of 17 patients treated with OKT3 (16 for acute rejection and 1 for cyclosporine toxicity), 11 pulmonary infections were observed (65%), 9 of which (53%) with onset within a mean of 9 days after OKT3 administration. The infections were severe in all cases and lethal in 8 cases: the most common pathogens were Candida (4 cases) and Pseudomonas aeruginosa (3 cases). On the contrary, of 39 cases of rejection treated with steroids, infections were observed in 3 cases only (8%). The 53% incidence of pulmonary infections in OKT3 patients, significantly higher than in the extant patients (19%), confirms OKT3 treatment as a strong risk factor for severe pulmonary infections. Furthermore, the occurrence of pulmonary edema was directly related to OKT3 administration in 7 OKT3 patients (41%), whereas only 20 cases (24%) occurred in the extant OLT patients (p < 0.001). OKT3-related pulmonary edema was always observed in hyperhydrated patients at the time of drug administration and it seemed to be related to the vasoactive myocardiotoxic agents released by damaged T-cells.