Slow-release formulations of salbutamol, used in asthmatic patients, may have few effects on cardiac rhythm. This study was designed to compare incidence and type of cardiac arrhythmias in a group of ten patients with stable bronchial asthma before and after 6 weeks treatment with a slow-release formulation of salbutamol. After a baseline spirometric and electrocardiographic evaluation, patients received placebo for a two-weeks period. At the end of this period patients repeated spirometry and carried out a 24-hour-ambulatory-E-Holter-monitoring. Subsequently, patients received for 6 weeks a treatment with a slow-release formulation of oral salbutamol. At the end of this period patients repeated spirometry, a 24-hour-ambulatory-EG-Holter-monitoring and potassium serum levels were controlled. We concluded from our study that, in patients with moderate bronchial asthma the treatment with an oral formulation of slow-release salbutamol may carry out a significant and durable bronchodilator effect, without causing important cardiac arrhythmias.