The dose-related effects of dobutamine (DOB) on the contractility of fatigued diaphragm were studied in 16 anesthetized, mechanically ventilated dogs. The animals were divided into two groups of eight: the control (group C) and the DOB (group D). Diaphragmatic fatigue was induced by intermittent supramaximal electrophrenic stimulation at a frequency of 20Hz applied for 30min. Diaphragmatic con- tractility was assessed from changes in transdiaphragmatic pressure (Pdi). After the induction of diaphragmatic fatigue, Pd~ at low-frequency (20-Hz) stimulation decreased signifi- cantly compared with the prefatigue values (P < 0.05), whereas no change in Pdi was observed at high-frequency (100-Hz) stimulation. In group D, after producing fatigue, Pd~ at 20-Hz stimulation increased significantly with a continuous infusion of DOB (5 and 10 ~tg.kg z-rain-l) i.v. (P < 0.05). The P~ at 100-Hz stimulation increased significantly with adminis- tration of DOB 10~tg.kg-l.min -1 i.v. (P < 0.05). There was a significant correlation between dose of DOB and Pd~ at both stimuli (P < 0.05). In group C, the speed of Pa~ recovery at 20- Hz stimulation was relatively slower. The integrated diaphrag- matic electric activity (Edi) in each group did not change at any frequency of stimulation throughout the study. It is concluded that DOB increases the contractility of fatigued diaphragm in a dose-dependent manner.