We re-examined 158 subjects from a group of 226 previously normal persons who had received head and neck irradiation, 113 with elevated plasma thyroglobulin levels at their first visit and 113 with normal levels. Twenty-four subjects had thyroid scintigrams that had changed in the follow-up interval of 24 to 60 (mean = 45.3) months. Twelve subjects subsequently had thyroidectomy, and five malignancies were found. In the other 12 the changes tended to be more subtle, but in nine they very likely represented thyroid nodules. We conclude that the prevalence of radiation-induced nodules is not decreasing. More changes (17 of 24) occurred in subjects who initially had elevated plasma thyroglobulin levels (p less than 0.05). However, the difference was not significant when the analysis was limited to the almost certain development of a nodule. Longer follow-up will be needed to ascertain whether a high thyroglobulin level predicts a greater risk of developing thyroid nodules.