This proposal represents a comprehensive in-depth approach to a common pediatric diagnostic problem, the infant with acute onset of wheezing, in a collaborative research environment. The objectives are to improve current diagnostic capabilities for patients presenting with acute episode of wheezing under 3 years of age and to evaluate the role of and clinical consequences of specific viral infections in this age group. This study proposes to use viral diagnostic studies and selected immunologic studies to expand the "routine" diagnostic evaluation of patients presenting with this problem. Methods used for viral diagnostic studies include attempts at viral isolation from naso pharyngeal and/or throat and rectal swabs and viral serology. Selected immuno-logic studies include: quantitation of serum immunoglobulins (IgG, IgA, IgM by radial-immunodiffusion and IgE by radioimmunoassay), scratch and intradermal allergy skin testing, and serum radioallergosorbent studies for specific allergens. The utility of each of the proposed viral diagnostic or immunologic studies will be evaluated to determine the potential for improving diagnostic accuracy or prognostic indicators of future onsets of wheezing.