There is increasing evidence that diaphragm fatigue is a major cause of failure in weaning patients from mechanical ventilation. Patients in intensive care units are often administered dopamine to improve renal blood flow without regard to its effect on diaphragm blood flow. The aim of this study was to investigate if intravenous low-dose dopamine, equivalent to the dose used in intensive care units, can treat and prevent diaphragm fatigue. Diaphragm fatigue was produced in anesthetized rats by inspiratory resistance loading (IRL). The effect on diaphragm shortening, diaphragm blood flow, and aortic blood flow was determined. When diaphragm fatigue was attained, group I was given saline for 30 min while maintaining IRL. At the time of diaphragm fatigue, group II was given low-dose dopamine (2 microg/kg/min) for 30 min while maintaining IRL. In group III, dopamine administration was started before and continued throughout the period of IRL. Administering dopamine after the development of diaphragm fatigue (group II) increased diaphragm performance as measured by increased diaphragm shortening and was accompanied by an increased diaphragm blood flow. Administering dopamine prior to and throughout IRL (group III) prevented diaphragm fatigue. Low-dose dopamine can prevent and/or reverse diaphragm fatigue in rats without a significant change in aortic blood flow. This effect of dopamine may be due to increased oxygen delivery associated with the increased diaphragm blood flow, resulting in less free radical formation and thus less muscle damage.