Cytomegalovirus (CMV) infection in 28 adult patients after cord blood transplantation (CBT) from unrelated donors was compared with that after bone marrow transplantation from HLA (human leucocyte antigen)-matched related (R-BMT) and unrelated (U-BMT) donors. Positive CMV antigenaemia was seen in 19 (79%) of 24 CMV-seropositive patients at a median of 42 d (range 29-85 d) after CBT, but in zero of four CMV-seronegative patients. This did not differ significantly from values observed after R-BMT and U-BMT (66%, P = 0.22, and 60%, P = 0.15 respectively). Based on the antigenaemia results, 16 patients (67%) received pre-emptive ganciclovir therapy from a median of 47 d (range 36-67 d) after CBT. This proportion was higher than that observed after R-BMT (28%, P = 0.0048), but did not differ from that after U-BMT (50%, P = 0.21). In addition, the probability of requiring more than two courses of ganciclovir therapy after CBT (21%) was higher than after R-BMT and U-BMT (0%, P = 0.015 and 0.039 respectively). One patient (5%) developed CMV disease after U-BMT, whereas no patients developed CMV disease after CBT or R-BMT. The CMV serostatus, use of a steroid and HLA disparity affected the probability of requiring ganciclovir therapy after CBT (P = 0.024, 0.032 and 0.017 respectively). These results suggest that recovery of CMV-specific immunity after CBT is delayed when compared with BMT.