SUMMARY Bronchial hyperesponsiveness (BHR) is a characteristic feature of asthma which is present in virtually all asthmatics with current symptoms. Airway inflammation plays an important role in BHR. It has been suggested that some of the macrolide antibiotics have anti-inflammatory properties and are shown to be effective in the treatment of asthma. The aim of this study was to evaluate the effects of a new synthetic macrolide antibiotic, clarithromycin, on the BHR to metacholine in patients with asthma. We studied 40 patients with bronchial asthma under treatment (budesonide 400 mcg b.i.d. and salbutamol 200 mcg p.r.n. (up to two times weekly). Subsequently, in one group of 20 patients (8 males/12 females, aged 42±12 ) we added 250 mg of clarithromycin b.i.d. for 8 weeks. The remaining 20 patients (5 males/15 females, aged 41±16) constituted the control group. In one subgroup of patients who received clarithromycin, cortisol levels were determined. Results: The PD20 of patients who received clarithrornycin was 0,5887±0,564 and 1,7194±0,684 before and after treatment respectively (p<0,001). The respective values of PD20 for the control group were 0,436±0,41 and 0,3909±0,505 (p=ns). Cortizol levels remained unchanged. We conclude that, clarithromycin reduces the degree of BHR in patients with asthma. Pneumon 1999, 12 (2): 117-122