The present investigation was done to determine whether measles enzyme immune assay (EIA) absorbency values were lower in women born in the vaccine era after 1963 and their infants in an upstate New York metropolitan area, an area of low measles incidence during the past 10 years compared with women born before the measles vaccine era who had natural measles. Aliquots of 202 sera from mother-infant pairs collected for other purposes from November 1990 to June 1991 at Albany Medical Center Hospital were tested by EIA. The demographic data available for analysis were maternal age and infant gestational age. Measles mean absorbency values were analyzed according to maternal age. Of 202 mother-infant pairs, 30% of mothers and 17% of their infants were seronegative (EIA < 0.16). Mothers born before 1963 and their infants had significantly higher mean EIA absorbency values than mothers born after 1963 and their infants (P < 0.002). The percent seropositive for measles antibodies by EIA for mothers born before 1963 and their infants, 87% and 94%, respectively, was significantly higher than the percent seropositive for mothers born after 1963 and their infants, 61% and 69%, respectively (P = 0.0001). Since the mean measles antibodies as measured by EIA absorbency were significantly lower in the mothers born after 1963 and their infants compared with women born before the vaccine era, the strategy for measles control in the future may have to include lowering the age of infant immunization.