In 1962 Weller and Hanshaw reported evidence of the teratogenic potential of CMV (cytomegalic inclusion disease virus or cytomegalovirus) for the developing human embryo. Some other investigators have also shown that CMV may be involved in different pathological conditions, that it is an ubiquous agent capable of producing a high incidence of infection, usually asymptomatic, under quite diverse ecological conditions, and that the proportion of individuals that have been in contact with the virus increases with age, which is evidenced by the frequency of seropositivity to the specific antigen. The high prevalence of CF antibodies to CMV in the studied groups from the state of Chiapas, particularly in Lacanjá where 45% of the total population (120 inhabitants) was included in the survey, indicates a wide dissemination of this virus. Lower levels of seropositivity were found among children from the Mexico City group, but they are higher than those found in serological surveys in children from Huixquilucan (state of Mexico) and from Seattle and Dallas in U.S.A. The possible implications of some seroepidemiological characteristics of CMV infection are discussed.