Recent reports have shown that thyroid-stimulating immunoglobulins (TSI) may be detected by measuring cyclic AMP increases in cultures of isolated thyroid cells in response to added patient immunoglobulins (Ig). We have compared the frequency that TSI may be detected in the Ig fraction of 114 sera from 112 patients with a variety of thyroid disorders, to the presence of thyrotrophin binding inhibitor Ig (TBII). Whereas the sera of 46 out of 48 (95.6%) patients with untreated thyrotoxic Graves' disease had detectable TSI, only 26 out of 48 (54.2%) had detectable TBII. We did not find any significant correlation between TSI and TBII for these patients but there was a significant correlation between TSI and both serum T3 (r = +0.55, P less than 0.01) and T4 (r = +0.50, P less than 0.01). Twelve patients were studied at the time of relapse of thyrotoxicosis due to Graves' disease. All sera contained detectable TSI whereas only one contained detectable TBII. Of the sera from 20 patients in remission after antithyroid drug therapy three were positive for TSI. One of these samples as well as two others had detectable TBII. The two samples with TBII in the absence of TSI came from patients who had developed hypothyroidism. TSI were detected in the serum of one out of nine patients with Hashimoto's thyroiditis but not in the sera of 20 other patients with a variety of non-autoimmune thyroid disorders including five patients with thyrotoxicosis not due to Graves' disease. However TSI was found in the sera of three out of five patients with exophthalmos and no history of hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)