Zinc (Zn) deficiency may occur in a subset of CF children, which may potentially contribute to the impairment of their growth and immune functions. Many of the studies that investigated the status of Zn in CF relied exclusively on plasma Zn level-which is not a reliable indicator of Zn status in the body. In this study, we evaluated cellular and plasma Zn levels in both CF and control subjects. In addition, IL-2 production and several T lymphocyte subsets were also measured in both groups. A total of 16 CF patients and 17 age-matched normal subjects were included in this study. Zinc levels were assayed using flameless atomic absorption spectrophotometry, cellular IL-2 production was assayed by ELISA, and T cell subtypes were measured by flow cytometry. CF patients showed significantly lower granulocyte and lymphocyte Zn levels than normal subjects (P < 0.01). There was no statistical difference between the CF patients and the control subjects in their platelets and plasma Zn levels. There was also no difference between the two groups in the proportions of their T lymphocyte subsets. IL-2 production was higher in the normal subjects than in the CF patients (P β«Χ‘β¬ 0.05). Based on cellular Zn criteria, ten CF patients were classified as Zn-deficient. When compared to all the Zn-sufficient subjects in the study, the Zn-deficient CF patients had significantly lower IL-2 production (P β«Χ‘β¬ 0.03). In conclusion, our results showed that a mild Zn deficiency, manifested by low cellular Zn levels, can occur in a subset of CF patients, and this may lead to a reduction in their lymphocyte IL-2 production.