Inhaled formoterol fumarate, a long acting beta 2 agonist, produces bronchodilatation that is sustained for approximately 12 hours. To determine whether such bronchodilator effects are maintained and asthma control sustained during chronic administration, we monitored airflow indices and clinical control in 112 asthmatic patients who self administered formoterol twice daily for periods ranging from 9 to 12 months. Subjects were recruited immediately following completion of a 3-month double-blind comparison of formoterol, 12 micrograms, bid versus salbutamol, 200 micrograms, qid. Assessments were conducted at baseline, 3, 6, and 9 months, where baseline represents the final visit of the 3-month comparative study. Patients were asked to complete diary cards and twice daily PEFR for a 2-week period before each assessment. Throughout the follow-up study, there was no indication of worsening of asthma control or deteriorating lung function. For the patients who continued to receive formoterol, the previous improvement in asthma control and lung function was maintained at the level reached in the 3-month study. There was an improvement in flow rates and asthma symptoms in the group switched from salbutamol to formoterol by the first clinic visit. This improvement in asthma control and lung function was maintained over the subsequent 6 months. Formoterol was well tolerated during the study period. We conclude that prolonged use of formoterol fumarate twice daily results in sustained improvement in symptoms and flow rates in asthma with no evidence of tachyphylaxis.