To the Editor: Because the mothers and infants in their study were excreting the same strain of cytomegalovirus (CMV), Pass et al. (May 28 issue)1 infer that the mothers acquired the infection from their toddlers; most of the fathers were known to be seronegative. However, the direction of transmission was established by the chronology in only one of the seven pairs (not two, as stated in the text). We agree that it is likely that in some of these families the mother acquired the infection from her child, rather than vice versa. The important question is how often this occurs…. © 1987, Massachusetts Medical Society. All rights reserved.