To the Editor.
—We read with interest the article by Azizi entitled "γ-Glutamyl Transpeptidase Levels in Thyroid Disease" in the January Archives (1982;142:79-81). We have studied the serum GGT activity in 24 patients with untreated thyroid diseases—12 with hyperthyroidism (ten female and two male patients, aged 26 to 80 years; mean ± SEM, 58.16 ± 5.23 years) and 12 with hypothyroidism (eight female and four male patients, aged 12 to 70 years; mean ± SEM, 52.66 ± 4.81 years). A group of eight female and four male normal volunteers served as control subjects. Their mean ± SEM age was 35.91 ± 1.92 years. The diagnosis of thyroid disease was based on clinical findings and measurement of serum free thyroxine (T4) index and thyrotropin level. Serum GGT was assayed by a kinetic-spectrophotometric method according to Szasz.1 None of the patients or control subjects with conditions known to modifier serum