The parameters of thyroid function were determined in Akungba and Oke-Agbe communities of Akoko area, where goiter is endemic and compared to a control population of Erinmo and Ifewara in Ijesha area, both areas being in southwestern Nigeria. The two study areas have similar physical and geological settings. However, while the main carbohydrate source of the control population are yam and/or bread-fruit, the Akoko population derives her carbohydrates mainly from cassava which could lead to increased serum thiocyanate, a goitrogen. The serum level of tetraiodothyronine (T4) was significantly (P < 0.05) higher in Ifewara (11.0) and Erinmo (11.8) compared to Akungba (7.1) and Oke-Agbe (8.8[symbol: see text]micrograms/dL). The triiodothyronine (T3) was significantly (P < 0.05) higher in Ifewara (193) than Erinmo (133) and also significantly (P < 0.05) higher in Oke-Agbe (127) compared to Akungba (107 mg/dL). Conversely, thyroid stimulating hormone (TSH) (microU/mL) level was significantly (P < 0.05) higher than values obtained from Ifewara (4.5) and Erinmo (3.3). T3/T4 ratio above 25, indicative of hypothyroidism and endemic goiter, was 14, 7, 4 and 0% from Akungba, Oke-Agbe, Ifewara and Erinmo, respectively. The results of the present study clearly explain the Akoko goiter endemia in the light of modification (s) of thyroid metablism.