A large number of samples of human neoplastic and abnormal nonneoplastic tissues were studied by nuclear magnetic resonance spectrometry in order to evaluate the possible role of this technique in the diagnosis of cancer. The spin-lattice magnetic relaxation times (T1) of abnormal nonneoplastic tissue were longer, in many instances, than those of malignant tumors from similar sites, preventing recognition of the tumors in this manner. The evidence for the nonspecific nature of the prolongation of T1 in abnormal tissue is reviewed, and additional limitations of this technique in the diagnosis of cancer are indicated.