It is not clear whether the IgE system plays a role in the pathogenesis of Graves' disease which is an autoimmune disorder. The low-affinity receptor of IgE, which is known as CD23, is not simply a receptor, it has various functions related to immune cells. There is no information about its levels in Graves' disease. For these reasons, serum IgE and soluble CD23 levels were determined in 40 patients with thyroid disease, free from allergic disorders and/or parasitic infestations. Patients were divided into three groups: Group 1: Patients with Graves' disease (n = 15, age: 33.4 +/- 9.3, 9 women/6 men). Group 2: Patients with non-toxic diffuse or multinodular goitre (n = 15, age: 31.0 +/- 12.7, 13 women/2 men). Group 3: Patients with toxic nodular goitre (n = 10, age: 44.6 +/- 14.2, 9 women/1 men). There was no age or sex difference between the groups (p > 0.05). Serum IgE level was somewhat higher in group 1 as compared with the other two groups, but the difference was not statistically significant, the values showed great individual variations (Group 1: 99.60 +/- 105.10, Group 2: 47.89 +/- 53.42, Group 3: 46.48 +/- 35.90 IU/ml, p > 0.05). Serum sCD23 was detectable in 7 of 15 patients in group 1 (46.7%), 1 of 15 patients in group 2 (6.7%) and 1 of 10 patients in group 3 (10.0%). Serum sCD23 detectability ratio was found higher in patients with Graves' disease than in the other two groups (p < 0.02). Serum IgE levels were compared in sCD23 detectable and undetectable Graves' patients. The values were similar (sCD23 detectable group: 105.30 +/- 135.90, sCD23 undetectable group: 94.70 +/- 55.30 IU/ml, p > 0.05). These results suggest that increased detectability of sCD23 is associated with Graves' thyrotoxicosis. An underlying state of autoimmune thyroid disease may be a permissive factor for this phenomenon.