In a prospective study, the addition of dipivefrin hydrochloride 0.1% twice daily to one eye of 32 patients with early primary open-angle glaucoma or ocular hypertension, maintained on a bilateral beta 1-, beta 2-blocker twice daily, resulted in a significant decrease of mean intraocular pressure (IOP) from 22.7 +/- 3.9 to 20.2 +/- 3.4 mmHg at 1 week (P = 0.0001) and to 21.0 +/- 3.8 mmHg at 12 weeks (P less than 0.02) in the dipivefrin-treated eyes. On the other hand, no significant change was noted in the fellow eyes (from 21.7 +/- 4.1 to 21.6 +/- 4.0 mmHg at 1 week and to 21.3 +/- 4.2 mmHg at 12 weeks). The addition of dipivefrin resulted in an IOP reduction of 2 mmHg or more in 50% and 3 mmHg or more in 19% of the eyes throughout the 12-week therapy. The result of the current study provides a realistic guideline as to what to expect from the common practice of adding dipivefrin hydrochloride to a beta 1-, beta 2-blocker regimen.