SUMMARYPatients with endemic goitre in an iodine deficient area in the Territory of Papua and New Guinea (TPNG) have very little clinical evidence of hypothyroidism although serum thyroxine (T4) levels are usually very subnormal. The activities of T4‐binding proteins in both goitrous and non‐goitrous iodine deficient TPNG subjects were therefore investigated but no overall deficiencies were found to account for the low T4levels. The mean serum T4‐binding pre‐albumin (TBPA) level (169μg/100 ml as T4‐binding capacity) was less than the level seen in Australian subjects (187μg/100 ml); however, this decrease was counteracted by the increase in T4‐binding globulin (TBG) level (27±3μg) in iodine‐deficient TPNG compared with 19±9μg in Australia.Measurements of TBG and TBPA levels were also made during pregnancy in TPNG subjects, and found to increase to the same extent as in pregnancy in Australian subjects. This suggests that the pathogenesis of endemic cretinism (in TPNG) is dependent on some factor other than TBG deficien