Kawasaki syndrome and RSV infection are common illnesses that afflict infants and young children. Recent studies demonstrate that intravenous immunoglobulin (IVIG) treatment significantly reduces the clinical severity of these illnesses. The purpose of the current review will be initially to examine mechanisms of disease pathogenesis in KS and RSV infection. This will be followed by a discussion of the potential mechanisms by which IVIG acts in these two illnesses. In both KS and RSV prophylaxis, an important action by which IVIG may work is primarily through toxin or microbial neutralization resulting in the dampening or prevention of the inflammatory response. Other immunomodulatory actions of IVIG are likely to be operative in these diseases and will be an active area of future research.