Darbepoetin alpha (Aranesp®) is produced by gene-technology in Chinese Hamster Cells (CHO-K1). It has a biological effect and toxicity profile comparable to r-HuEPO; with the exception of a longer half-life which means that it can be administered less frequently without loosing clinical efficiency. Aranesp® has been well tolerated in studies conducted to this date. In this setting Aranesp® appears to be safe and well tolerated. Adverse events reported to date have generally been mild to moderate in severity and consistent with events and symptoms in cancer patients with chronic disease receiving chemotherapy (i.e. fatigue and gastrointestinal symptoms). Clinical studies have shown a higher frequency of thromboembolic reactions including deep vein thrombosis and pulmonary embolism in cancer patients receiving Aranesp therapy compared to patients receiving placebo. The clinical experience so far with Aranesp® has been published (15,16,17). Aranesp® is registered for clinical use in Europe and US.