In vitro analysis of spin-lattice relaxation times (T1), water self-diffusion coefficients (DH2O), and proton NMR spectroscopy were performed in a study of 88 patients with thyroid lesions in order to determine the usefulness of these parameters in the differentiation of benign and malignant tissues. Thyroid tissue sample proton NMR spectral patterns were examined at 360 MHz. Proton NMR spectra were different for normal thyroid tissues, benign, and cancerous lesions. Significantly prolonged T1 (0.5T) and decreased DH2O were found in cancerous thyroid lesions relative to normal thyroid tissues. Considerable overlap was found, however, in comparing T1 and DH2O values for benign and malignant thyroid lesions. This study suggests that proton NMR spectroscopy may be more useful than T1 and DH2O in differentiating benign and malignant thyroid lesions.