A total of 124 children of both sexes aged between 6 and 12 years with pollen-associated rhino-conjunctivitis were included in a multicentre double-blind study of parallel group design to compare the effects of cetirizine 10 mg daily, given as 5 mg morning and evening for 2 weeks, with those of placebo of identical appearance. Rhinorrhea, sneezing, nasal obstruction and nasal and ocular pruritus were evaluated using symptom scores by patients on daily self-evaluation cards and by investigators who, in addition, made a global evaluation at the end of treatment. Appropriate wash-out periods for previous medicines were observed. Unchanged treatment of asthma was allowed and inhaled corticosteroids were continued in 3 placebo patients. Compliance was checked and found to be less than 80% of the prescribed dosage in 2 cetirizine patients. The mean percentage of study days when symptoms were absent or at the most mild (i.e. present but not disturbing), as reported daily by the patients, was significantly greater with cetirizine (56.2%) than placebo (29.7%). This 26.5% difference was considered clinically significant. The value of this method of expressing treatment effects in allergic rhinitis is discussed. Improvement in maximum symptom scores (severest symptoms) assessed by investigators was better for cetirizine than placebo after treatment for 1 week and 2 weeks. Improvement in individual daily symptoms was greater for cetirizine than placebo after a few days.(ABSTRACT TRUNCATED AT 250 WORDS)