A multicentre, controlled trial was carried out to determine whether removal of leucocytes from blood by means of 'Imugard IG500' (Terumo) filters would prevent transfusion-acquired cytomegalovirus (CMV) infection in newborn infants. 72 infants whose mothers were seronegative and who received some seropositive blood were followed for 6 months for evidence of CMV infection. There were no significant differences between the groups who received filtered and unfiltered blood in median gestation, birthweight, or amount of seropositive blood received (median volume 32.5 ml and 34.5 ml, respectively). 9 (21%) of the 42 infants who received unfiltered blood and none of the 30 who received filtered blood were infected with CMV. All infected infants weighed less than 1500 g at birth; they represented 31% of very low birthweight (VLBW) infants at risk of CMV infection. None of 24 VLBW infants who received filtered seropositive blood was infected. 1 infected infant died and 5 had clinical features consistent with CMV infection. The results show that transfusion-acquired CMV infection is preventable by filtration of blood through a leucocyte filter. This method has advantages over other methods of removing leucocytes or the use of only seronegative blood for newborn infants.