Specific labeling of liver plasma membrane glucagon receptors has been achieved by the photoincorporation of a 125I-labeled photoderivative of glucagon, NE-4-azidophenylamidinoglucagon. Identification of glucagon receptors was facilitated by irradiating membranes in the presence of excess unlabeled glucagon. Isoelectric focusing of radioiodinated membrane proteins revealed one major band of glucagon displaceable material which had an isoelectric point of 5.85. When this material was isolated and run on SDS-polyacrylamide gels a major labeled band of Mr55000 was obtained which had properties consistent with those of the glucagon receptor. These studies indicate that a purification of the glucagon receptor of greater than 700-fold can be attained through the use of isoelectric focusing and SDS-polyacrylamide electrophoresis.