1. The regional haemodynamic effects of i.v. bolus doses of atrial natriuretic peptide (ANP, 1 and 10 nmol), calcitonin gene-related peptide (CGRP, 0.05 and 0.5 nmol) and corticotropin-releasing factor (CRF, 1 and 5 nmol) were assessed in conscious Long Evans and Brattleboro rats chronically instrumented with miniaturized, pulsed Doppler probes. 2. The low dose of ANP was without effect on mean arterial pressure (MAP), but caused tachycardia and hindquarters vasodilatation with vasoconstriction in renal and mesenteric beds in Long Evans rats. With the high doses of ANP these effects were more pronounced and MAP fell. In Brattleboro rats there was a primary renal vasodilatation. 3. The low dose of CGRP caused a slight fall in MAP in Long Evans rats, tachycardia and a renal vasodilatation. The high dose of CGRP caused marked hypotension, tachycardia and renal, mesenteric and hindquarters vasodilatation in both strains of rat. However, only in Long Evans rats were there secondary renal and mesenteric vasoconstrictions. 4. The low dose of CRF caused falls in MAP in both strains of rat, accompanied by renal and, particularly, mesenteric vasodilatation. Administration of the high dose of CRF caused profound, prolonged hypotension, tachycardia and mesenteric vasodilatation. There was also (late onset) hindquarters vasodilatation accompanying renal vasoconstriction that followed the initial vasodilatation in this vascular bed. 5. These results indicate that appropriate doses of particular peptides may be capable of promoting flow through individual peripheral vascular beds.