Thirty-one immunocompromised patients with severe cytomegalovirus (CMV) disease were treated with intravenous ganciclovir. Twenty-one patients had received transplants - 15 bone marrow recipients, five renal allograft recipients, and one liver transplant recipient - while the other ten were immunocompromised due to acquired immunodeficiency syndrome (six), hematologic malignancies (three), and systemic lupus erythematosus (one). They presented with one or more of the following syndromes: CMV pneumonitis (19), CMV of the gastrointestinal tract (six), CMV retinitis (seven), and CMV hepatitis (three). Seventeen (55%) of 31 patients demonstrated clinical improvement during ganciclovir therapy, with the best response seen in the transplant recipients. Viremia ceased in 14 (93.3%) of 15 patients after a mean of 4.7 days of therapy; viruria ceased in eight (53.3%) of 15 patients after a mean of 11 days of therapy. Ganciclovir plasma concentrations at a dosage of 2.5 mg/kg/three times a day were as follows: mean peak, 16.04 μmol/L; mean trough, 2.38 μmol/L. Neutropenia occurred in 11 (35%) of 31 patients and in nine (60%) of 15 bone marrow transplant recipients. We conclude that ganciclovir exerted an antiviral effect against CMV and may play a role in the treatment of CMV disease in patients with depressed immunity, especially bone marrow and organ transplant recipients.