We investigated the effects of long-term instillation of bunazosin hydrochloride--alpha 1 specific adrenergic antagonist--on the aqueous humor dynamics and blood-aqueous barrier in rabbit eyes. We examined intraocular pressure, aqueous flow rate, and blood-aqueous barrier permiability for albumin after four weeks application of 0.05% bunazosin. The effect of bunazosin on blood-aqueous barrier destruction by laser iridophotocoagulation was also examined. During four weeks, bunazosin reduced the intraocular pressure by 1.7 +/- 0.6 mmHg (mean +/- SEM). Continuous application of bunazosin had no significant influence on aqueous flow rate and fluorescein isothiocyanate-labeled rabbit albumin (FITC-Alb) concentration in the anterior chamber. Bunazosin had no effect on the rise of the FITC-Alb concentration after iris photocoagulation, but the intraocular pressure in bunazosin treated eyes was significantly lower than in control eyes one hour after photocoagulation.