The influence of several factors on 186Re-BLM formation is investigated by means of Sn(II) reducing method. The results show that the labelling yield is mainly dependent on the pH value in reaction medium
and that sodium gluconate is a suitable protecting agent to avoid Re-oxidation of the reduced Re. The method for preparing 186-BLM is described with labelling yield up to 98% in the pH range from 3 to 4.5.