The aim of the investigators study is to compare in children aged less than 18 months and hospitalized for an acute viral bronchiolitis the efficacy of the HS 3% (Mucoclear®, sterile ampoules of 4 ml) nebulised with a conventional jet-nebulizer (particles diameter of 4-5 µm), or with a jet-nebulizer adapted for infants (particles diameter of 2-2.5 µm), or with a mesh-nebulizer adapted for infants (particles diameter of 2-2.5 µm).

Inclusion Criteria:

• Infant of less than 18 months old
• infant hospitalized for a 1st episode of bronchiolitis defined as a 1st episode of respiratory difficulty with sibilant and\or crépitants in a viral context (head cold and\or cough and\or fever and\or notion of contage)
• Necessity of an clinical score upper to 4. This clinical score, described by Wang in 1992, is the clinical score classically used in the studies concerning the acute(sharp) bronchiolitis of the infant ( 8,9,12 ). He(it) is at most on 12 points.
• absence of respiratory décompensation requiring an admission in Unity of Pediatric Intensive care
• signature of the Informed consent
• Membership in a national insurance

Exclusion Criteria:

• Refusal of the parents to participate in the study
• 18-month-old infant hospitalized for acute(sharp) bronchiolitis with a clinical score lower than 4.
• signs of respiratory décompensation requiring a transfer in resuscitation, signs of hypercapnie or episodes of apneas
• histories of bronchiolitis or asthma of the infant
• cardiac underlying pathology, respiratory, neuromuscular, immunodeficient or former premature of less of 34 weeks of amenorrhoea and less than 3 months of corrected age.
• child having set within 6 hours preceding the inclusion a treatment by bronchodilatateurs or corticoids by systematic or inhaled way.