The pathogenesis of nasal polyps has been debated for many years. The lymphocytes that infiltrate nasal polyps have been identified as predominantly memory T cells in an activated state, and these cells produce a mixed cytokine pattern of T1 helper (Th1) and T2 helper (Th2) cells. We conducted a prospective study to compare the expression levels of some Th1 and Th2 cytokines in atopic and nonatopic patients. Our study population consisted of 75 adults-42 men and 33 women (mean age: 38 yr)-with nasal polyposis. Patients with an allergy were distinguished from those without an allergy on the basis of the history, the results of skin-prick testing, and measurement of total IgE serum concentrations. Based on these criteria, patients were divided into two groups: atopic (n = 38) and nonatopic (n = 37). Levels of cytokine gene expression in the atopic patients were compared with those of the nonatopic patients by real-time polymerase chain reaction. Statistical analysis found no significant differences in the rate of interleukin (IL) 10 and IL-12 gene expression between the allergic and nonallergic patients. On the other hand, rates of interferon gamma and IL-4 gene expression were significantly higher in the atopic patients (p = 0.03 and p = 0.02, respectively). Our research suggests that an imbalance of Th1 and Th2 cells plays an important role in the pathophysiology of nasal polyps. Although nasal polyposis is a multifactorial disease associated with several different etiologic factors, chronic persistent inflammation is undoubtedly a major factor, regardless of the specific etiology.