To determine if ganciclovir given three times per week post-transplant is tolerable and effective for prevention of cytomegalovirus (CMV) infection in recipients of T cell-depleted marrow from related or unrelated donors, we have used ganciclovir 2.5 mg/kg iv three times daily on days -8 to -2 and 5 or 6 mg/kg iv 3 times per week from engraftment to day 100 as CMV prophylaxis for 51 adults who were CMV-seropositive or had seropositive donors. All patients received iv immunoglobulin 500 mg/kg weekly and CMV-negative or filtered blood products. Blood and urine were tested for CMV at weekly intervals through day 100. All patients received ganciclovir pre-transplant. Ten patients did not receive ganciclovir post-transplant (5 deaths, 3 graft failure, 1 renal failure, 1 required foscarnet). The median time to initiation of ganciclovir was 27 days (range 17-59 days) and the median duration of therapy was 51 days (range 5-83 range). Twelve patients had dose reductions (3 neutropenia and 9 renal insufficiency). Seven patients died before day 100, 2 had indications to change to foscarnet, 15 discontinued ganciclovir because of neutropenia and 17 completed the full ganciclovir course through day 100. G- or GM-CSF was given to 29 patients with neutrophils < 1.5 x 10(9)/l (10 had neutrophils < 0.5 x 10(9)/l) but only 12 of them could continue full-dose ganciclovir. Bacteremia occurred in 12 of the neutropenic patients. At day 120, the actuarial rate of CMV infection was 58% (95% CI 42-74%) and that of CMV disease was 36% (95% CI 21-51%).(ABSTRACT TRUNCATED AT 250 WORDS)