The aim of this study was to investigate the efficacy and tolerability of intranasally applied dimetindene (CAS 3614-69-5) 0.1% spray in children suffering from seasonal allergic rhinitis. A total of 100 children under 14 years with acute seasonal allergic rhinitis participated in this randomised, single-blind, reference-controlled, multi-center, parallel group study with two treatment groups. The study took place between 2nd April and 16th September 1996 during the pollen season. Patients were examined at enrollment (day 1), day 8 and day 15. Patients kept diary throughout the 2-week treatment phase. Patients were randomised to receive either dimetindene 0.1% (Fenistil Nasal Spray) or a levocabastine (CAS 79516-68-0) 0.05% solution as reference medication. Both medications were supplied in similar outer packages. A single-blind approach was chosen, because the reference medication levocabastine requires two spray puffs per nostril as a single dose, whereas for dimetindene maleate solution a single spray puff per nostril is sufficient. Dimetindene 0.1% was applied with 1 spray puff (= 0.14 mg dimetindene) in each nostril and levocabastine with 2 spray puff (= 0.10 mg levocabastine) in each nostril every day in the morning before leaving the house and in the evening before going to bed. Additional administration of the spray was allowed up to 4 times a day if needed. Efficacy was assessed as change in severity of characteristic symptoms associated with pollen rhinitis: nasal rhinorrhea, nasal itching, nasal sneezing and nasal congestion. In addition, changes in ocular symptoms, lacrimation, ocular itching and red eyes, global physician's assessment of efficacy at the end of treatment were assessed. The primary criterion change of total nasal symptom severity score between day 1 and day 3 resulted in a statistically equivalent and therapeutically relevant symptom reduction for the two treatments. All secondary criteria showed a similar reduction in symptoms, thus underlining the consistency of the findings. Both nasal sprays were well tolerated. It is concluded from these results that dimetindene 0.1% nasal spray solution is a safe and efficient treatment option for children under 14 years suffering from seasonal allergic rhinitis.