In our investigator-initiated prospective study, a total of 170 children with at least two episodes of wheezing and a first degree family history of atopic disease were recruited from our walk-in clinic between October 2002 and October 2004. We chose this relatively long period of time to exclude a seasonal selection bias (e.g., upper airway infections or airborne allergens). 131 eligible children (6 to 24 month old) were randomly assigned to a double-blind dietary supplementation with Lactobacillus rhamnosus strain GG ATCC 53103 (LGG) twice daily or placebo over six months. A computerized randomization schedule was prepared by a biostatistician with allocation and dispensing of capsules by the distributor of LGG. The capsules were matched for size, shape, and volume of content, which was reconstituted with 5 ml water and then given by spoon. Compliance was monitored by use of a capsule chart (completed by parents) and capsule counts. The parents were asked to keep a diary provided by the study group. Clinical monitoring was done for one year: before the intervention (visit 1), after 3, 6, 9, and 12 months (visit 2 to 5). It encompassed episodes of asthmatic exacerbations defined as cough and wheeze, numbers and days of associated hospitalizations, symptom free days, days without use of rescue medication (steroid suppositoria, a frequently used device in Western Europe), and associated inhalative steroid and beta-agonist use. Children underwent a physical examination including determination of the severity scoring of atopic dermatitis (SCORAD) index to assess eczema severity examination on each study visit to our walk-in clinic. To ensure consistency, the same investigator performed all SCORAD assessments. Atopic eczema was confirmed by characteristical cutaneous findings, pruritus, and chronic relapsing course. This last criterion was fulfilled if the child presented eczema for at least one month on at least one visit. Asthma diagnosis was based on an algorithm from an international paediatric asthma consensus group. Asthma was diagnosed if the child had chronic or recurrent cough, wheeze or shortness of breath, or both, and if other diagnosis were excluded and trial antiasthmatic treatment was effective. Blood samples were taken on visit 1, 3, and 5. Sensitization to common dietary and respiratory allergen was measured by total and antigen specific IgE assays against hen’s egg, cat epithelia, house dust mite (D1+2), birch pollen, milk protein, lactalbumin, timothy pollen, horse epithelia and alternaria by chemiluminescence-immunoassay. This highly-sensitive assay is suitable especially for the determination of low value of specific IgE. Additionally, eosinophilic cationic protein and eosinophils were determined.