Doppler tissue imaging is a new technique of measuring the velocities of myocardial wall motion. In order to assess its value in the diagnosis of acute rejection, the velocities of the interventricular septum and left ventricular posterior wall were measured in systole and early diastole in 34 cardiac transplant patients at the time of their endomyocardial biopsy, using an M mode left parasternal short axis view. During 40 episodes of acute rejection (26 mild and/or moderate, 10 sub-severe and 4 severe), the wall velocities decreased significantly (p < 0.001) both in the interventricular septum and endocardium of the posterior wall. Myocardial velocities were significantly slower in sub-severe or severe rejection than in mild or moderate rejection. The most sensitive criterion was the measurement of posterior wall endocardial velocity in early diastole, a decrease of 10% having a sensitivity of 92% whereas the sensitivity of usual Doppler echocardiographic parameters is only 73%. Acute rejection, even mild cases, can be diagnosed with excellent sensitivity by measuring myocardial velocities by Doppler tissue imaging. This technique has the advantage of being non-invasive, reproducible and reliable in the follow-up of cardiac transplant patients.