Liquids from radioimmunoassay (RIA) are low-medium activity wastes as well as potentially infectious since they may contain pathogens from patients' blood. Present management of these wastes consists of temporary storage for activity decay and later disposal by an authorized company. In spite of activity decay, these wastes cannot be discharged due to chemical and biological content, and they have to be managed after decay according to these characteristics. This paper proposes the treatment of these wastes by membrane technology (ultrafiltration and reverse osmosis). The purposes of the treatment are: removal of radioactivity and pathogens to make decontaminated liquid suitable for discharge; and volume reduction of final waste. Experiments with real RIA wastes of different activity levels were performed. According to experimental results, the most suitable treatment protocol is defined, from the point of view of activity removal. (C) 2013 Elsevier B.V. All rights reserved.