Glaucoma is a potentially blinding disease. The goal of glaucoma therapy is to reduce intraocular pressure to a predetermined target level. There are currently 5 classes of compounds used for the medical management of glaucoma. Four classes that appear promising for the long term management of glaucoma are in different phases of clinical investigation, and include the topically active carbonic anhydrase inhibitors, selective alpha 2-adrenergic agonists, prostaglandins and ethacrynic acid. The topically active carbonic anhydrase inhibitor dorzolamide (MK-507) is effective and well tolerated in clinical trials of up to 1 year's duration. Animal studies have demonstrated that this drug lowers intraocular pressure by reducing aqueous humour formation. The selective alpha 2-adrenergic agonists, brimonidine and apraclonidine, have been shown to be effective in reducing intraocular pressure in the short term. Long term effectiveness of these agents is under investigation. Prostaglandins (PG) of the PGF2-alpha isopropylester series caused marked reductions of intraocular pressure in laboratory and clinical trials. The newest prostaglandin analogue, latanoprost (PhXA41), effectively lowered intraocular pressure and was well tolerated in clinical trials of up to 4 weeks' duration. Prostaglandins reduce intraocular pressure by enhancing uveoscleral outflow. Ethacrynic acid enhanced traditional outflow facility and lowered intraocular pressure when applied topically or intracamerally in laboratory studies and clinical trials. Corneal adverse effects of ethacrynic acid have been noted. Reformulation of ethacrynic acid ointment may resolve this problem. These 4 classes of compounds will enhance our options for the medical management of glaucoma. They may be used instead of or in combination with some of the drugs currently in use, and may be better tolerated.