The serum T4=T4(D), T3 in vitro uptake=RT3U and TSH were measured before and 30 min after the injection of 200 mug of TRH in 30 subjects from an iodine deficient area of Central Greece. These persons were divided in two groups of 16 goitrous and 14 nongoitrous patients and the results from each group compared to each other and also with the same parameters obtained from 14 controls subjects, all nongoitrous and from a nonendemic area. It has been found that in this area with a mild iodine deficiency serum T4 is the only hormone decreased whereas RT3U and TSH both before and 30 min after TRH injection are normal. There existed however a negative correlation between serum T4 and TSH in the goitrous group. Why the nongoitrous iodine deficient persons achieve the same compensation without thyroid gland enlargement remains unsolved but it may be stated from the present results that goitre development should be regarded as a maladaptation rather than a compensatory process.