We have evaluated thyroid and thyrotropin functions before the beginning and during Growth Hormone (GH) treatment for a 2-6-year period in a group composed of 21 children (age: 6.6 +/- 1.1 years, m +/- SD) suffering from classic GH deficiency. Circulating levels of thyroxine, and basal thyroid-stimulating hormone (TSH) always resulted in the normal range. TSH response to thyreotropin-releasing hormone administration showed in some subjects (one out of 21 before the start of treatment, 2 out of 16 after 2 years, 3 out of 12 after 4 years and 2 out of 10 after 6 years) a delayed (after 90-120 minutes) and higher peak in comparison to that of normal subjects. All these high and delayed values have been showed in only one occasion by different children, with the exception of a child who has presented the higher values in two occasions. Growth response to GH treatment has not been modified by the change in thyrotropin response, as subjects with high TSH peak have had a height velocity similar to that of the other children in the corresponding periods of study.