Human T-lymphotropic virus type l (HTLV-l) in cord blood raises the possibility of intrauterine transmission as an alternative pathway to transmission via breast milk. However, none of 7 children with HTLV-l proviral DNA positive cord blood had seroconverted by 24–48 months. Contamination of cord blood by maternal blood was precluded on the basis of viral load and lgA concentration. Thus cord blood proviral DNA is not a hallmark of intrauterine infection. Moreover, none of the cord blood samples of 9 formula-fed children later confirmed to be infected was positive for HTLV-l, indicating that intrauterine infection is not likely candidate as an alternative pathway. Lancet 1994; 343: 1326–27