[Show abstract][Hide abstract] ABSTRACT: Preclinical studies demonstrated that erythropoietin is neuroprotective in different models of peripheral and central nervous system diseases. We investigated safety and tolerability of recombinant human erythropoietin (rhEPO) in amyotrophic lateral sclerosis (ALS). We performed a phase II double-blind, randomized, placebo-controlled study. After screening, 23 patients were randomly assigned to rhEPO or placebo arm. Patients were examined during a six-month lead-in period, and then they received fortnightly either 40,000 units of rhEPO or placebo for 24 months. Primary outcomes were adverse events, safety, and death or tracheotomy. Treatment was safe and well tolerated. One patient in the rhEPO arm dropped out for a superficial phlebitis. Median values of haematocrit, haemoglobin, red cells, and reticulocytes were non-significantly higher in rhEPO than placebo arm. Haemoglobin did not increase >1 g/dl between subsequent doses. Anti-rhEPO antibodies were not detected. Survival and slope of ALSFRS-R curves did not significantly differ between treatment groups. RhEPO treatment was safe and well tolerated in ALS patients. Our results suggest that larger studies are warranted to confirm safety of treatment and to investigate different dose schedule and efficacy.