In the present study T3, T4, TSH serum concentrations were measured in 166 subjects whose goiter grading was ascertained according to WHO classification; 39 of them had no goiter (grading 0), 127 were goitrous with a grading comprised between 1a and 4. The two samples were composed by Males and Females of various ages whose choice was strictly predetermined by random numbers. The median ages of 127 goitrous and 39 non goitrous subjects were respectively 23.5 years and 33.5 years; 30 Males and 5 Females were in the first group; 58 Males and 69 Females in the second. They lived in the Ouham region of Centro African Republic where some of the Authors ascertained a severe goiter endemia due to iodine deficiency and manioc consumption as staple food. All the values of T4 and TSH of the two group of subjects, were significantly different from the control values (p less than 0.01) excepting T3. Goitrous subjects had T4 value lower than non goitrous subjects (p less than 0.05). The subjects of each group were distributed in the four subsequent subgroups: A) with T3, T4, TSH in the normal range; B) with elevated TSH and T3 and T4 in normal range; C) with elevated TSH, subnormal T4, and T3 in normal range; D) with elevated TSH and subnormal T3 and T4. From fig. 1 it can be seen that the 79.5% of goitrous subjects had a supranormal TSH (subgroups B + C + D) and 40.7% of them had a subnormal T4 (subgroups C + D).(ABSTRACT TRUNCATED AT 250 WORDS)