Interactions between cytokines play an important role in the development of thyroid autoimmunity. Using enzyme-linked immunosorbent assay we investigated serum concentrations of soluble interleukin-2 receptor (sIL-2R), interferon-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-10, CD30, monokine induced by interferon-gamma (MIG), cytotoxic T lymphocyte antigen-4 and markers of apoptosis decoy receptor 3 and Bcl-2 in 28 patients with hyperthyroid Graves' disease (GD), 24 patients with untreated Hashimoto's thyroiditis (HT) and 15 healthy controls. TNF-alpha, IL-10 and sIL-2R were higher in GD compared with HT and controls (TNF-alpha: 8.79 in GD versus 2.54 pg/ml in HT, P = 0.01; IL-10: 10.00 versus 3.10 versus 3.10 pg/ml, P(1) < 0.001, P(2) = 0.005; sIL-2R: 1.26 versus 0.64 versus 0.46 ng/ml, P < 0.001). MIG and CD30 were higher in HT compared with controls (649.22 +/- 262.55 versus 312.95 +/- 143.35 pg/ml, P = 0.037, 6.57 +/- 2.35 versus 3.03 +/- 1.04 U/ml, P = 0.036 respectively). In GD sIL-2R decreased when the euthyroid state was achieved (1.31 +/- 0.64 versus 0.260 +/- 0.11, n = 12, P < 0.001). sIL-2R correlated positively with free thyroxine (FT4) (R = 0.521, P = 0.000) and negatively with thyroid stimulating hormone (TSH) (R = -0.472, P = 0.00132). MIG correlated negatively with FT4 (R = -0.573, P = 0.00234) and positively with TSH (R = 0.462, P = 0.0179). The results suggest that serum concentrations of sIL-2R and MIG are related to thyroid function rather than to activation of autoimmunity.