The effect of topically active 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) eye-drop formulations containing solutions of acetazolamide, ethoxyzolamide or timolol on the intra-ocular pressure (IOP) was investigated in normotensive conscious rabbits. Both acetazolamide and ethoxyzolamide were active but their IOP-lowering effect was less than that of timolol. The IOP-lowering effects of acetazolamide and ethoxyzolamide and that of timolol appeared to be to some extent additive. Combination of acetazolamide and timolol or ethoxyzolamide and timolol in one HP-beta-CyD formulation resulted in a significant increase in the duration of activity compared with HP-beta-CyD formulations containing only acetazolamide, ethoxyzolamide or timolol. Also, it was possible to increase the IOP-lowering effect of acetazolamide by formulating the drug as a suspension in an aqueous HP-beta-CyD vehicle.