Topical atenolol (a beta1-adrenoceptive antagonist), pilocarpine, and placebo were tested in a randomised double-blind crossover trial of 8 patients with ocular hypertenion. Atenolol (2% 3 times a day) caused a fall in intraocular pressure (IOP) comparable to that achieved by topical application of pilocarpine (2% 3 times a day). The decrease in IOP by each compound was demonstrable on the second day of application and was significantly (P is less than 0.05) reduced on the seventh and 14th days of treatment. The combination of 2% pilocarpine and 2% atenolol administered 15 minutes apart (3 times a day) lowered the IOP significantly from the second day of treatment, and this reduction persisted throughout the trial period of 14 days. This combined of treatment, treatment lowered the IOP more than either substance alone. However, this further decrease was statistically significant only on the 14th day of treatment (atenolol versus atenolol + pilocarpine, P is less than 0.05). No change of the episcleral venous pressure was observed after 14 days' treatment with either atenolol or pilocarpine alone, or combined.