We made a comparative survey of the poliovirus antibodies (anti-poliovirus type 1, anti-poliovirus type 2 and anti-poliovirus type 3) and the measles antibodies in malnourished but completely vaccinated children (37) and control children (34). The age range was 10 months to 5 years. Immunization in children with protein-energy malnutrition was low for both vaccines. Seroprevalence rates of the polio 1, polio 2, polio 3 antibodies and the measles antibodies in the control group were 94.1%, 97.1%, 91.2% and 82.4% respectively. In malnourished children the respective rates were in some cases significantly lower being: 40.5% (P = 0.001), 59.5% (P = 0.001), 40.5% and 35.1%. Malnutrition is a major determinant of the humoral response to oral polio and measles vaccines and must be given due consideration to prevent vaccination failure.