The regional haemodynamic profiles of Ro 31-6930, cromakalim and nifedipine were compared using pulsed Doppler flowmetry in the anaesthetised rat. In order of potency, Ro 31-6930 (0.1–300 μg/kg), cromakalim (1–300 μ/kg) and nifedipine (1–1000 μ/kg) produced dose related falls in mean arterial pressure. The hypotensive effects of Ro 31-6930 and cromakalim were accompanied by reflex tachycardia. All three agents reduced renal vascular resistance by 30–50%. Cromakalim exerted a selective action on this vascular bed. Similar maximal reductions in mesenteric vascular resistance (37–50%) were observed; however, cromakalim was the least potent on this vascular bed. Maximal reductions in iliac vascular resistance (65–78%) were observed, with an order of potency as observed on mean arterial pressure. Qualitative differences in the regional haemodynamic profiles of Ro 31-6930, cromakalim and nifedipine are evident from this study. The different profiles of Ro 31-6930 and cromakalim may reflect structural differences between the pharmacophores of these compounds.