The serum PB127I was measured in 291 people (113 men and 178 women) in two population surveys of elderly people living at home. The plasma inorganic iodine (P.I.I.) was measured in 39. No convincing evidence was found of a significant prevalence of undiagnosed hypo- or hyperthyroidism in the elderly community, nor was there evidence of widespread iodine deficiency. The tests of thyroid function used in the present study do not appear to have a useful place in the routine screening in healthy elderly people. Further study to determine the cause of unsuspected low and high PB127I values in the presence of clinical euthyroidism is indicated.