Résumé : Rationale. The bronchodilating potency of magnesium sulphate (MgSO
4) has been shown in acute asthma exacerbations. We hypothesized that smooth muscle cell relaxation by magnesium might also be beneficial in chronic severe asthma with persistent airflow limitation. Aim. To investigate whether nebulised magnesium, administered according to a dosing scheme shown to be effective in acute asthma, induces bronchodilation in stable asthma patients with persistent airflow limitation. Methods. In a placebo-controlled, cross-over study, 13 severe asthma patients with postbronchodilator FEV
1 < 75% predicted received either 2.5 mL MgSO
4 6.4% or placebo in 3 nebulisations at 30 minute intervals. Before the first and 30 minutes after the last inhalation FEV
1, exhaled nitric oxide (NO) in dyspnoea (Borg) were measured. Results. After MgSO
4 treatment no improvement in FEV
1 occurred (56.2 ± 16.8 to 55.4 ± 17.4% predicted [p = 0.5]), neither was a change in exhaled NO or Borg observed (p > 0.1). The changes in FEV
1, NO or Borg were not different between the treatment arms (p ≥ 0.09). Conclusion. Short-term treatment with magnesium inhalations had no direct bronchodilating effect in stable severe asthma patients with persistent airflow limitation. Yet, clinical observations suggest a heterogeneity in response, probably related to treatment intensity, and support further exploration of magnesium administration in these patients.