Duplex doppler examination of blood flow in renal interlobar arteries was analysed in twelve critically ill patients before and during low-dose dopamine infusion (2 micrograms/kg/min). Renal vasodilatation and increased blood flow were observed with dopamine, confirming results with indirect or invasive techniques. The doppler ultrasound technique is entirely non-invasive, is simple and quick to carry out, provides instant results, and will allow tailoring of inotropic support in critically ill patients to provide optimum renal blood flow.