Two series of experiments were undertaken to identify the topological location of the structural polypeptides of Epstein-Barr virus. In the first series of experiments, nucleocapsids prepared by detergent treatment of enveloped virus with Nonidet P-40 and sodium deoxycholate were found to be composed of seven polypeptides, VP2, 6, 7.5, 24, 27, 31, ANd 33, which ranged in molecular weight from over 200 X 10(3) to 28 X 10(3). Nine other polypeptides, VP 4, 7, 8, 10, 15, 16, 23, 28, and 29, could be identified in preparations of Epstein-Barr virus nucleocapsids, but the relative amount of this second group of polypeptides was less in preparations of nucleocapsids than in preparations of enveloped virus. The incomplete removal of these polypeptides from enveloped virus by detergent treatment suggests that some of these polypeptides may be components of the envelope or tegument that lie in close proximity to the outer surface of the nucleocapsid In the second series of experiments periodic acid-Schiff-staining and glucosamine-containing components were identified with similar electrophoretic mobility to several of the polypeptides of enveloped virus (VP 5, 8, 9, 11, 12, 13, 14, 15, 16, 17, 28, and 29) that were completely or incompletely removed from purified virus preparations by detergent treatment. The similarity between the polypeptide composition of the nucleocapsids of Epstein-Barr virus and herpes simplex virus was in contrast to the dissimilarity between the nonnucleocapsid polypeptides of Epstein-Barr virus and herpes simplex virus.