Myocardial proton T2 relaxation measurements were performed on five normal subjects over 4 weeks (20 measurements) and on nine heart transplant recipients (35 measurements). All magnetic resonance measurements were performed with a 1 T system. All patients had endomyocardial biopsy the same day as magnetic resonance imaging. Results of biopsies were normal on 32 occasions and abnormal three times (two cases of acute rejection and one case of myocardial edema). T2 values for normal subjects were 46.6 +/- 8.1 and 46.9 +/- 4.9 msec (septum and left ventricular free wall, respectively). T2 values for transplant recipients with normal results of biopsies were 44.5 +/- 7.8 and 43.1 +/- 7.5 msec. T2 values in three patients with abnormal results from biopsies were elevated (69 +/- 7.6 msec, range 59.7 to 77.6 msec). The results show similar values in normal subjects and transplant recipients with normal results from biopsies. Increased T2 values in three patients with abnormal results from biopsies indicate that relaxation time measurements may be of value to identify patients at risk of rejection.