Two synthetic analogues of angiotensin II (ANG II) with an extended N-terminus, (Sar)5-ANG II and (Pro)3-ANG II, have been tested in vitro for their ability to bind to ANG II receptors, to raise cytosolic free calcium concentration, [Ca++]i, and to induce a biological response in bovine adrenal zona glomerulosa cells and in cultured rat aortic smooth muscle cells. The results indicate that the two analogues did not behave identically in these two target cells for ANG II. On one hand, in the adrenal cortex, (Sar)5-ANG II and (Pro)3-ANG II were very weak agonists and (Sar)5-ANG II could even be used as an antagonist of ANG II-induced aldosterone production. On the other hand, both peptides were almost as potent as ANG II in vascular smooth muscle cells, with respect to signal messenger generation and prostacyclin synthesis. Such peptides may be useful tools in the elucidation of the differences among ANG II receptors from various target tissues.