The magnetic resonance imaging (MRI) characteristics of evolving hemorrhage are discussed and compared with those of computed tomography (CT). Studies of 15 hematomas were undertaken in four mongrel dogs. The hematomas were created by the injection of autologous blood into the subcutaneous tissues of the thigh. The hematomas were studied serially with both MRI and CT. Pulse sequences included spin-echo (2100 msec TR, 40 and 80 msec TE) and inversion-recovery (2100 msec TR, 400 msec TI, 40 msec TE). Relaxation times (T1 and T2) were calculated in each case. CT values (H) were also obtained. In addition, 24 single and 14 serial scans of hemorrhage were obtained from 24 patients. MRI was performed on a 0.15-T resistive magnet scanner. T1 and T2 relaxation times and CT values decreased as the hematomas resolved. T1 and T2 relaxation times of intraparenchymal hemorrhage tended to remain elevated with time. MRI seems to be more sensitive than CT for the detection of hemorrhage, primarily because of superior contrast resolution.