Safe doses of low-intensive visible, class (II) He-Ne laser of = 632.8 nm in a dose response of (12-84) J/cm 2 has been used for investigating laser effects on thyroid gland function of rabbits. Thyroid gland function was examined by monitoring and determining the triiodothyronine (T 3), thyroxin (T 4) and the thyroid stimulating hormone TSH level before (as controls) and after laser irradiation. The activity of Thyroid Glad for (T3) and (T4) production increase directly with laser exposure

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... tion while the rate of TSH production decreases by the same rate. The correlation of T 3 , T 4 and the TSH hormones production during laser irradiation also studied con-firing our data is the closely correlated that obtained for three hormones investigated.