The question as to whether or not topical medication with beta blockers causes a decrease in tear production remains unanswered. Earlier studies using filter-paper strip tests have yielded contradictory results. In the present study, computerized objective fluorophotometry was used to assess the effect of topical medication with 0.5% timolol (b.i.d.; OU) on tear volume and tear production in 24 consecutive patients with bilateral primary open-angle glaucoma. Tear-film fluorophotometry was performed before treatment as well as at 7 days, 14 days, and 4-7 months after the onset of treatment. The results showed that by 7 days after the initiation of timolol treatment, both tear volume (-29%, P < 0.01) and tear secretion (-36%, P < 0.01) had decreased significantly. However, at both 14 days and 4-7 months after the onset of treatment, none of the values differed significantly from those obtained before treatment. Thus, topical antiglaucomatous treatment with 0.5% timolol eye drops leads to a transient decrease in tear production. This effect, however, lasts no longer than 14 days after the beginning of treatment.