Angiotensin II (Ang II), an octapeptide produced by cleavage of angiotensinogen by angiotensin-converting enzyme, plays a fundamental role in cardiovascular homeostasis. Two GPCRs, AT1 and AT2, mediate the effects of AngII. Most of the known actions of angiotensin II are mediated through the AT1 receptor and serve to maintain blood pressure and glomerular filtration rate in the face of extracellular volume depletion (Griendling et al. 1996). In vitro and in vivo studies indicated that the AT2 receptor counterbalances the effect of the AT1 receptor (Horiuchi et al. 1999). Expression of the AT2 receptor is developmentally regulated: it is highly expressed in various fetal tissues and at a lower density in adult adrenal medulla, brain, and reproductive tissues (Griendling et al. 1996). AT2 expression appears to be re-expressed or up-regulated after vascular injury, myocardial infarction, cardiac failure or wound healing (Matsubara 1998). AT2 membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of agonists and antagonists of AT2. The membrane preparations exhibit a Kd of 0.53 nM for [125I]-CGP42112. With 0.25 nM [125I]-CGP42112, 5mg/well AT2 Membrane Prep typically yields greater than 50-fold signal-to-background ratio.