The absorption of timolol after topical administration to the eye was studied in 11 healthy volunteers and in 5 patients with bilateral open angle glaucoma. The volunteers received 2 drops of 0.5% timolol ophthalmic solution in each eye, equivalent to 0.8mg of timolol maleate. Overflow was absorbed by paper tissue. The patients received the same dose twice daily for 2 weeks and were then investigated. In the paper tissue, 12 to 88% of the dose administered was recovered. Plasma concentrations were never above 5ng/ml and not always detectable (detection limit 1 to 2ng/ml). However, timolol was absorbed as the drug was found in the urine samples from all volunteers and glaucomatous patients.