Management of severe acute asthma attacks in children sometimes bring difficulties to the physician. Some current treatment strategies have focused on intravenous magnesium sulphate administration in patients nonresponding to therapy with beta-2 agonists and corticosteroids. The use and efficacy of this drug has been discussed in this randomized, double-blind, placebo-controlled clinical trial consisting of 20 children with moderate to severe acute asthma exacerbation admitted to the emergency department in Dicle University Hospital, Turkey. Magnesium sulphate infusion therapy of 40 mg/kg doses (maximum 2 g) or an equivalent volume of normal saline solution were administered to randomly assigned 10 patients in each group to the selected patients who were being treated for an acute asthma exacerbation with a peak expiratory flow rate (PEFR) less than 60% of the predicted value after receiving three beta-2 adrenergic nebulizer treatments (salbutamol) given at an interval of 20 minutes each. Vital signs, PEFR and physical examinations were serially recorded at 15 minutes intervals for a total of 90 minutes after the initiation of magnesium sulphate therapy. At 30 minutes, compared with the placebo group, the magnesium sulphate receiving group had lower clinical asthma scores (4.0+/-0.5 vs. 5.5+/-0.5, p = 0.0002) and a significantly greater percentage of improvement from baseline in PEFR (43.0+/-6.3% vs. 14.6+/-3.7%, p = 0.0002). These significant changes persisted at 45, 60, 75 and 90 minutes. No significant side effects were observed. In conclusion, severe asthmatic cases may benefit from magnesium sulphate therapy when beta-2 agonists are inadequate in preventing deterioration.