We conducted a prospective study of 60 patients in a tertiary care referral center to ascertain the status of cell-mediated immunity as determined by delayed hypersensitivity reactions in patients with nasopharyngeal carcinoma (NPC) or allergic rhinitis. Delayed hypersensitivity as detected by Mantoux testing is generally accepted as a reflection of the level of cell-mediated immunoactivity-the less hypersensitivity reaction that occurs, the lower the level of immunoactivity is, and vice versa. Our study population was made up of three groups: 20 newly diagnosed patients with NPC (pretreatment), 20 age- and sex-matched patients with allergic rhinitis, and 20 matched controls without either disease. A negative Mantoux test (0- to 5-mm induration) was seen in 13 patients with NPC (65.0%), in 17 patients with allergic rhinitis (85.0%), and in 16 controls (80.0%); none of these differences was statistically significant. However, it is interesting that while the NPC group had the lowest percentage of negative Mantoux results overall, it had the highest percentage of patients who had no reaction at all (i.e., 0-mm induration); a complete absence of any reaction was seen in 7 of the 13 Mantoux-negative NPC patients (53.8%), compared with 2 of the 17 Mantoux-negative allergic rhinitis patients (11.8%) and 3 of the 16 Mantoux-negative controls (18.8%). An absence of a reaction generally indicates a very limited degree of cell-mediated immunoactivity. Therefore, we conclude that patients with NPC appear to have significantly less cell-mediated immunity than do patients with allergic rhinitis and normal controls; no statistically significant difference was noted between the latter two groups.