We have evaluated the efficacy of cetirizine in 24 patients (18 males and 6 females, mean age 25.4 years) suffering from mild or moderate allergic asthma due to grass pollen. Cetirizine was given once a day at the dosage of 10 mg for four weeks. On a daily card patients had to record the number of asthmatic attacks, the usage of bronchodilatators and the values of peak expiratory flow measured in l/min in the morning and at the evening. The improvement of the parameters considered was statistically significant, and no side effects have been observed. Cetirizine is therefore an effective and safe drug in the treatment of mild and moderate asthma induced by grass pollen.