This study investigates possible detrimental effects on the immune system of Inuit infants which may be induced by prenatal and postnatal (breast feeding) exposure to persistent environmental contaminants such as organochlorine compounds. These substances accumulate in the body of Inuit women in part due to their consumption of sea mammal fat and can be transferred to the foetus during pregnacy and to the infant during breast feeding. Immune system function will be evaluated using several parameters: 1) the level of antibody produced by the infant following Haemophilus influenza immunization; 2) the level of proteins which protect the infant against bacterial infections (complement system) before its immune system is fully developed; and 3) the level of chemical messengers (cytokines) which enable the various cells of the immune system to communicate with each other, thereby maintaining its proper function and assuring the protection of the infant against bacteria, parasitic and viral infections.