The prevalence of thyroid gland “hot spots”--areas which are hyperavid for 131I--is reported for several samples of euthyroid and otherwise normal subjects. A longitudinal study, in progress for 12 years, sought to determine the fate of the hot spot over time, and to ascertain whether or not changes in the hot spot are related to life strain. The results suggest that such a relationship exists and that lige strain, usually prolonged and severe, may stimulate the hot spot to progress on to clinical thyrotoxicosis.