NMR imaging of rats with implanted hepatomas in the liver demonstrates that under the imaging conditions of this study tumors of over 8 mm2 in area can be detected with high accuracy. Compared to normal liver, approximately 70% of these tumors had a combination of relaxation times (T1-T2) that could be uniquely identified as tumors, while the other 30% demonstrated relaxation time combinations that overlapped those previously found for abscesses, brain, and hematomas.