The iv administration of TRH has been associated with side effects, such as nausea, flushing, and urinary urgency. However, few reports mention changes in blood pressure. This study defines the mean and range of the blood pressure responses in 70 euthyroid patients subjected to iv administered TRH. The mean increase was 21.0 +/- 1.4 mm Hg for systolic and 13.9 +/- 1.0 mm Hg for diastolic blood pressure; however, individual peak values increased as much as 56 and 42 mm Hg, respectively. Thus, the hemodynamic response to iv administered TRH can be quite severe in some subjects, and caution is suggested in selecting patients for testing.