Timolol maleate, a non-selective beta-adrenergic blocker, has been used to treat glaucoma and ocular hypertension for almost two decades. Recently a new preparation, timolol hemihydrate, has been described which eliminates the maleate buffer and simplifies the purification step for the R-enantiomer. The ocular pharmacology of the two medicines is expected to be similar. Ocular bioavailability as well as toxicity for timolol hemihydrate is similar to that which has been shown previously for timolol maleate. In a multicenter trial in the United States, timolol hemihydrate was shown to reduce the intraocular pressure to a similar extent as timolol maleate. At the week 12 visit intraocular pressure was 19.5 and 19.5 mm Hg for the hemihydrate and maleate groups respectively for the 0.25% concentration and 18.3 and 18.6 mm Hg respectively for the 0.5% concentration. Following a nine month open-label portion where patients were treated with timolol hemihydrate only intraocular pressure was 19.9 and 19.1 mm Hg for the 0.25% and 0.5% concentrations respectively. Ocular and systemic adverse events, as well as vital signs, were similar between timolol hemihydrate and maleate. In conclusion, timolol hemihydrate appears to be a safe and effective medicine in the treatment of ocular hypertension and chronic open-angle glaucoma.