The effect of natural mucosal priming on systemic and mucosal immune responses was investigated in young children after parenteral influenza vaccination. Eighteen young children and 8 adults were vaccinated with trivalent influenza vaccine at various time intervals before tonsillectomy. The influenza-specific IgG, IgA, and IgM immune responses were examined in tonsillar lymphocytes and frequent samples of peripheral blood and oral fluid. Young children were divided into primed and unprimed groups on the basis of presence of prevaccination serum antibodies. In peripheral blood, adults and primed children had significantly higher IgG and IgA antibody responses than did unprimed children. Irrespective of priming, children elicited weaker IgA responses than adults in both tonsils and oral fluid. While natural priming was essential to elicit strong systemic response in young children after parenteral influenza vaccination, it did not influence the local responses, which were significantly lower in both primed and unprimed children than in adults.