Introduction: In the recent years, a considerable attention has been paid to the problem of nitrates due to their intensive use as agricultural fertilizers which reach to humans and animals by different routes.
Purpose: To validate the toxic effects of nitrates in a short-term experiment (60 days) on thyroid gland and the possible ameliorative effect(s) of vitamin C.
Materials and methods: Thirty two adult male albino rats were divided into four groups: group I (control) received distilled water, group II received 500mg∕kgvitamin C, group III received 130mg/kg sodium nitrates (NaNO3) and group < strong> IV received 130mg/kg NaNO3 plus 500mg∕kgvitamin C.All supplementations were taken as oral single dose daily for 60 days.At the end of experiment, blood samples were subjected to hormonal assay (T3, T4 and TSH serum levels).  Also, thyroid glands' specimens were prepared for the optical and electron microscopic examination.
Results: I- The biochemical analyses showed a significant decrease in serum T3 and T4 and a significant increase in TSH.
II-Light microscopic examination of nitrates treated group revealed disturbed thyroid architecture in the form of heterogeneous poorly developed follicles. Enlarged deformed follicles with scanty vacuolated colloid, degenerative empty follicles and some fused follicles with exfoliated cells filled their lumen were observed.
III-Electron microscopic examination showed stratification of follicular epithelial cells. Most of the follicular cells appeared with irregular nuclei, dilation of rER, many vacuoles and an apparent number of lysosomes.  Also hypertrophy and hyperplasia of parafollicular-C cells were observed. An improvement of thyroid gland's structure, ultrastructure and function was observed in vitamin C added group.
In conclusion: This study concluded that nitrate is a thyroid gland disruptor via a mutual interdependence between the follicular, parafollicular and intra-thyroidal mast cells. The supplementation of vitamin C showed beneficial effects upon biochemical and patho-morphological alterations, developed in thyroid gland following exposure to toxic doses of nitrates. So, the recommendations are limitation of sodium nitrates uses, encourage dietary intake of vitamin C and routine analysis of thyroid function in the most nitrates' contaminated areas.