The antibodies to measles and rubella viruses were titrated in a sample of infantile population in Palermo in 1978. Measles antibodies were investigated in 900 children aged 0-15 years by the HI test; rubella antibodies in 120 girls aged 12-14 years by the hemolysis-in-gel test. A "saturation" level of immunity against measles virus as can be found in the adult population appeared to be attained at the age of 12-13 years. At this age however, about 28% of the girls were still not immunized against rubella virus.