Prior to the availability of sensitive TSH assays, thyrotropin releasing hormone (TRH)stimulation tests were relied upon for confirming and assessing the degree of suppressionin suspected hyperthyroidism. Typically, this stimulation test involves determining basalTSH levels and levels 15 to 30 minutes after an intravenous bolus of TRH. Normally,TSH would rise into the concentration range measurable with less sensitive TSH assays.Third generation TSH assays do not have thislimitation and thus TRH stimulation is generally not required when third generation TSHassays are used to assess degree of suppression.