To evaluate the importance of trace amounts of elements in thyroid cancer etiology and diagnostics, instrumental neutron activation analysis has been used to estimate Ag, Co, Cr, Fe, Hg, I,Rb, Sb, Sc, Se, and Zn concentrations in malignant and benign thyroid nodules as well as in apparently intact paranodular thyroid tissue. Resected material from 135 patients was obtained from operations. Forty-five cancer cases were diagnosed and the rest were of benign nodules. The thyroid glands of 65 people, 53 male and 12 female, who died and unexpected death or committed suicide, were used as a control group. Trace element contents of the International Atomic Energy Agency reference material H-4 (animal muscle) were analysed simultaneously with the thyroid tissue in order to evaluate the accuracy of the obtained data. No dependence of trace element contents on sex and age (14-80 years) was found for normal thyroids. In paranodular tissue, the Ag, Co, Hg, I and Rb contents were much higher for malignant and benign nodules than they were for the standard. There was also a slight deficiency of Se in the nodules compared with the standard. This result supports the hypothesis that the direct toxic heavy metal influence on thyrocytes plays a major role in thyroid cancer etiology, provided that an adequate level of the defence mechanisms is absent. Iodine concentrations are 15 times lower, on average, in malignant compared with benign nodules. It is also shown that the radio between the iodine concentration in nodular and paranodular tissue can be used for in vivo thyroid cancer diagnostics.