The present work reports the clinical and laboratory findings in two endemic areas in Niger: Tiguey-Tallawal and Belley-Koira. The goitrous subjects (n = 293), mainly children and adolescents, have clinical evidence of euthyroidism but with biological criteria of hypothyroidism in 25% of cases as shown by the decrease of the total serum T4 and the increase of serum TSH. Iodine deficiency intake evaluated by the determination of urinary iodine in single urine specimens is the permissive and main factor for goiter endemicity = 14 +/- 7 micrograms/l in Belley-Koira (n = 99), 26 +/- 23 micrograms/l in Tiguey (n = 155) and 25 +/- 19 micrograms/l in Tallawal (n = 95). The single intramuscular injection of iodized oil (240 mg of iodine) constitutes an extremely effective way of correcting iodine deficiency: decrease of volume or disappearance of goiter among 291 subjects out of 362 i.e. 80%, twelve months after the injection. The diffuse goiter, more numerous (n = 270) than nodular goiter (n = 92) are corrected with more efficiency (85% versus 50%). We also noted that non goitrous subjects living in these two endemic areas show a severe iodine deficiency (urinary iodine: 33 +/- 18 mu/l; n = 70 = 76) while those living in non endemic areas present a moderate or a low iodine deficiency, respectively in Niamey (urinary iodine: 48 +/- 36 micrograms/l; n = 200) and in Tamou (urinary iodine: 80 +/- 29 micrograms/l; n = 69). Severe, moderate and low iodine deficiency seem to be correlated with nutritional habits: mil in endemic areas, mil and meat in Niamey and mil, meat, milk and fish in Tamou. The nutriments eaten in Niger have a low iodine level except ewe milk: salt (270 to 7100 micrograms/kg), woman milk (40 +/- 21 micrograms/l) cow milk (22 micrograms/l) goat milk (50 micrograms/l), ewe milk (294 micrograms/l). Salt consumption, evaluated by the determination of urinary chloride, is adequate. Prophylaxis by iodinated salt should be well accepted. No other factors than iodine deficiency in the etiology of endemic goiter, mainly nutritional (goitrogens or protein-calorie malnutrition) can be evoked to explain clinical and biochemical discrepancies between subjects living in the same morbid territory.