Shedding of cytomegalovirus (CMV) was studied in 142 women who gave birth to congenitally infected infants and in 81 seropositive control mothers (mothers of uninfected infants). Viral cultures from the throat, vagina, and urine were obtained at intervals between one month and nearly 12 years after delivery. In both groups the prevalence of excretion of CMV was greater in younger women and fell to low levels by age 30. Considering all of the sites of infection, 60% of the mothers of infected infants were shedding CMV within the first three months post partum compared with 18% of the control mothers; CMV shedding rates declined during the first 12 months post partum to 35% in the former group and to 3% in the latter. More than three years after delivery, seven (15%) of 45 mothers who transmitted CMV still had viruria. The excretion of CMV is common and persistent in mothers of children with congenital infections due to CMV.