The study population will include the children attending the Pediatric Emergency Department of Oulu University Hospital because of respiratory infection and bronchial obstruction that is not relieved with conventional treatment. After written consent from the parents, the children will be randomized to get either intravenous magnesium sulfate or isotonic NaCl. The primary outcome is RDAI (Respiratory Distress Assessment Instrument) scoring six hours from the infusion. Secondary endpoints are RDAI scoring and oxygen saturation at other time points and length of hospital stay.