The objectives of the present study were to estimate the effects of increasing levels of the goitrogenic alliloisothiocyanate on body weight, thyroid hormones, morphology of thyroid follicles, and serum lipoproteins concentration. Twenty-four, growing male rats of Wistar strain were randomly assigned to four experimental groups (I – 0, II – 2, III – 4, and IV – 6 mg alliloisothiocyanate per kg body weight). For 20 days the rats were fed restricted amounts of AIN’93G diets and had free access to distilled water. Animal body weight was recorded weekly. No visible signs of alliloisothiocyanate toxicity were observed in this study. Feeding graded amounts of alliloisothiocyanate to rats resulted in insignificantly decreased serum concentrations of fT₄ (by 30.5%). No significant effect of dietary alliloisothiocyanate on TSH concentrations was noted. In addition, alliloisothiocyanate altered thyroid follicle morphology as indicated by both hyperplasia and hypertrophy of the follicular epithelial cells. Goitrogenic alliloisothiocyanate was found to decrease serum total cholesterol and serum LDL-cholesterol (24% and 30%, respectively).