A total of 71 patients with documented birch and grass pollen allergy participated in this randomized, double-blind, parallel-group study initiated to compare the long-term therapeutic efficacy of twice daily levocabastine, a new topical H1-receptor blocker, with that of sodium cromoglycate four times daily in the treatment of pollen-provoked conjunctivitis. There was no statistically significant difference in therapeutic efficacy between the two treatment groups, although a positive trend in favour of levocabastine was observed. Global evaluations of therapeutic efficacy were similar in both treatment groups. A total of 94% of levocabastine-treated patients rated treatment to be excellent or good compared with 86% of patients in the sodium cromoglycate group. Moreover, there were no significant differences in the severity of allergic symptoms reported on the patient diary cards. Patients were permitted to use rescue medication (oral terfenadine and betamethasone nasal spray) if symptoms became severe. The use of rescue medication was lower in the levocabastine group than in the sodium cromoglycate group. The mean number of days on which rescue medication was used was 12.8 and 26.9 in the two groups, respectively. The incidence, and type, of adverse reactions was similar in both patient groups. Levocabastine is well-tolerated and at least as effective as sodium cromoglycate in the treatment of pollen-provoked conjunctivitis.