Increased intraocular pressure (IOP) has been identified as the most important risk factor for the development and the progression of glaucoma. Data from large interventional studies have shown that a decrease of IOP is associated with a reduced risk of progression of the disease. This underlines the importance of a potent and save IOP lowering therapy. The introduction of preservative free tafluprost offers a new treatment possibility using a potent topical prostaglandin analogue without the disadvantages of a co-administered preservative. The current study seeks to investigate the effect of an 8 week therapy with preservative free tafluprost on intraocular pressure in patients with ocular hypertension or primary open angle glaucoma having an IOP of 30 mmHg or more.