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Neonates are highly susceptible to bacterial infections, which represent a major source of mortality and morbidity in this age category. It is recognized that β2 integrins play a critical role in innate immunity by mediating leukocyte vascular adhesion, transmigration and bacterial phagocytosis. Therefore, we aimed to assess if the impaired immune functions seen in newborns may derive, in part, from a transient insufficient β2 integrin expression. In the present study we measured baseline lymphocyte function-associated antigen-1 (LFA-1 or CD11a/CD18), macrophage-1 antigen (MAC-1 or CD11b/CD18) and leukocyte integrin p150-95 (CD11c/CD18) expression on cord blood, and on the third day of life in a cohort of 35 healthy neonates, compared with a control group of 12 healthy adults. For any of the three β2 integrins, the expression on polymorphonuclear cells was significantly lower on cord blood than in adults and increased from birth to day 3. We also compared superoxide radical (SR) production in these neonates with 28 non-smoking adults. SR production in response to integrin stimulation by Zymosan was significantly lower at birth than in adults, and it decreased further in the third day of life. These findings suggest that innate immune impairment in newborns may be, in part, accounted for by a lower β2 integrin expression on phagocytes in the neonatal period, but also by a functional impairment of free radical production.