Serologic status of about 300 subjects (age: 2-15 years) for measles, rubella, varicella and mumps was compared with the anamnestic recall of their mothers. Measles, rubella and varicella antibodies were determined by ELISA methods. Mumps antibodies were titrated by hemagglutination-inhibition test. Serology agreed with the clinical history of the subject in 83% of the cases for measles, in 69% for rubella, in 87% for varicella and in 82% for mumps. The frequency of seronegative subjects who were reported to have had the disease was low (less than 8%) for each of the four viruses. The opposite situation was found in the 8% of the subjects for measles, in 23% for rubella, in 10% for varicella and in 13% for mumps. In general there was no significant difference in the rate of disagreements between serology and history of the disease in relation to mothers' schooling and occupation (house wives or mothers who work outside the home). Geometric mean titers of hemagglutination-inhibiting antibody to mumps virus sharply declined 3-4 years after the disease and stabilized thereafter. Prevalence of antibodies according to age shows that measles, rubella and varicella antibodies are acquired early in life, while 29% of the subjects 14-15 years of age still lacked mumps antibodies.