The influence of thyroid hormones on the immune system is controversial. We analyzed the cytokine expression pattern of T lymphocytes in patients with severe nonimmune hypothyroidism in order to establish the role of thyroid hormones on the immune system. The study comprised 7 patients (1 male and 6 females) 20 to 76 years of age (mean age, 53 years), without signs of chronic thyroiditis, verified by histology and laboratory data. The patients were studied 5 weeks after total thyroidectomy. Peripheral blood mononuclear cell (PBMC) cultures and intracellular cytokine detection by flow cytometry before and after thyroid hormone replacement therapy were performed (free thyroxine [FT4] 0.030 +/- 0.034 ng/dL, versus FT4: 2.16 +/- 0.68 ng/dL). The control group consisted of 7 healthy subjects (FT4: 1.20 +/- 0.21 ng/dL). We found no significant differences in the cytokine pattern (interferon [IFN]-gamma, IL-2, interleukin [IL]-4, IL-5, IL-6, IL-10, IL-13, tumor necrosis factor [TNF]-alpha, TNF-beta) of CD4+ and CD8+ between the matched groups (hypothyroid subjects versus controls, levothyroxine treated subjects versus controls). Our data show no change in the type 1/type 2 balance of peripheral CD4+ and CD8+ T lymphocytes from patients with nonimmune hypothyroidism. According to our results, the hypothyreotic state does not contribute to the reported changes in cytokine production patterns in Hashimoto's thyroiditis.