PIP: Recent epidemiological surveys have demonstrated the association between malnutrition and infectious diseases. Parasitic infections, diarrhea, pneumonia, hepatitis and tuberculosis are more frequent and most serious in undernourished people and in infants with low birth weight. Data suggest an increased susceptibility to infectious diseases in individuals with protein-energy malnutrition and with iron-deficiency anemia; circulating lymphocytes and intraepithelial lymphocytes are also reduced in cases of malnutrition. Due to impaired immunological response, the effectiveness of prophilactic vaccination is doubtful in undernourished people; there have been, for example, reports of geographical variations in the response of children to polio virus vaccine. A whole series of strategies must be taken into consideration to break the vicious circle of malnutrition-infection; some of these are: breastfeeding; an improved schedule of vaccinations; nutritional supplement, especially for hospitalized patients; and prevention of low birth weight.