The objectives of the present study were to estimate the effects of increasing levels of the dietary intake of nitrites on: (1) urinary iodine excretion, 2) changes in the morphology of thyroid follicles, and 3) thyroid gland hormonegenesis, in laboratory rats. Effects of nitrites on serum lipoproteins were examined as well. Feeding graded amounts of nitrites to rats resulted in: (1) decreased iodine absorption in the digestive tract as indicated by decreased urinary iodine excretion, (2) altered thyroid follicle morphology as indicated by both hyperplasia and hypertrophy of the follicular epithelial cells, (3) altered metabolism of thyroid hormones as indicated by decreased serum concentrations of fT₄ and tended to increase serum concentrations of TSH, and (4) decreased total cholesterol and HDL in serum and tended to increase serum triacylglycerols. Therefore, nitrite may be considered a competitive iodine inhibitor, affecting the thyroid-pituitary hormonal axis, in a way similar to that of iodine deficiency, thus acting as a goitrogen. In addition, dietary nitrite tended to elevate serum LDL-cholesterol and triacylglycerol concentrations, and to decrease serum HDL-concentrations, hence inducing an atherogenic lipoprotein profile.