Pompe disease (Glycogen storage disorder type II) is an inherited disease because of a lack or reduced activity of the enzyme alpha-1,4-glucosidase (acid maltase). Since 2006, an intravenous enzyme replacement therapy (ERT) with Myozyme((TM)) (Genzyme Corporation, Cambridge, MA, USA) is available. Four adult patients aged between 39 and 68 years received ERT over a period of 6 months. Clinical and functional parameters were registered longitudinally. In three patients, a considerable improvement of symptoms could be noticed, patients with pre-existing respiratory insufficiency seemed to profit most. In all patients, a continuous decrease of initially raised laboratory parameters (creatine kinase, lactic dehydrogenase, transaminases) was striking. Enzyme replacement therapy seems to be a long-term effective therapy in adult patients with Pompe disease. Whether all patients will profit from an improvement of symptoms or at least a stabilisation of the otherwise progressive disease is currently not definitively clear.