['\u2002 Allergen-specific IgE antibodies are implicated in allergic diseases while allergen-specific IgG antibodies have been proposed to prevent allergic reactions. The objective for this study was to study whether the immune response (IgG and IgG4) to peanut differs in IgE-sensitized and non-sensitized young children.', '\u2002 A total of 239 children have been followed prospectively from birth to 5\u2003yr of age. The levels of IgG and IgG4 to peanut, Ara h 2, and Ara h 8 were analyzed at 2 and 5\u2003yr of age and related to IgE sensitization and peanut consumption.', '\u2002 The levels of peanut-specific IgG and IgG4 were significantly higher in peanut-sensitized children at 2 and 5\u2003yr of age when compared with non-sensitized children and children sensitized to other food/inhalant allergens. A strong correlation was seen between levels of peanut-specific IgG/IgG4-ratios and peanut-specific IgE at 5\u2003yr of age. Children avoiding peanuts, a subgroup of the peanut sensitized, had statistically significant higher levels of IgE to peanut and a tendency of higher IgG and IgG4 levels to peanut. In the avoidance group, significant correlations between IgE and IgG/IgG4 to peanut were found compared with children eating peanuts.'] Is peanut sensitization during the first 5 yr of life associated with elevated levels of peanut-specific IgG?