With the use of an immunofluorescence technique Epstein-Barr viral capsid antigen antibody titers were determined in the sera from 226 Sudanese: 41 with nasopharyngeal carcinoma (NPC), 77 with other head and neck cancers, 21 with malignant lymphomas, 63 with other cancers, 6 with specific granulomas, and 18 normal controls. Of the NPC patients, 87.8% had titers of 320 or greater and 43.9% had titers of 2,560 or more, whereas none had titers of less than 40. Their geometric mean titer (GMT) level was 1,855. However, compared to the NPC patients, the other patients and normal controls showed significantly higher percentages of sera with low titers and lower percentages of sera with high titers and they had a GMT that was 4--16 times lower. The high NPC titers were independent of age, sex, tribe, or locality of patients. The preliminary results indicated the importance of future immunovirologic and immunogenetic field investigations on the natural history of the Epstein-Barr virus and on the genetics of the host.