Affinity purification of the opioid receptor in NG 108-15 cells was carried out using an affinity resin based on the avidin-biotin interactions, but a new elution method was employed with a radioligand of sub-micromolar concentration. A synthesized biotinyl derivative of leucine-enkephalin has a high affinity for the delta-receptor, but the affinity was lowered 10-fold in the presence of avidin. The new elution method is based on this affinity decrease and resulted in a 100-fold purification over the initial crude materials in the single step. SDS-polyacrylamide gel electrophoresis of the purified receptor revealed three polypeptides of 58, 65 and 71 kDa as possible components of the delta-receptor.