Aim: this work was done with the aim of studying the probable relationship between follicular and parafollicular cells in drug induced hypothyroidism and hyperthyroidism by propylthiouracil and L thyroxine and consequently their effects on bone.Material and methods: the present work was carried out on 40 adult male albino rats, divided into 5 groups. Group I (control), group II (hypothyroid): rats that received propylthiouracil orally at a daily dose of (50 mg./kg/day) for 4 weeks, group III (hyperthyroid): rats that were given oral L-thyroxine at a daily dose of (40 µg/100gram /day) for 4 weeks, group IV (recovery hypothyroid) and group V (recovery hyperthyroid) rats that sacrificed 1 month after cessation of the drugs administration. Thyroid glands were examined using light microscopy and immunohistochemichal technique. Specimens of the right-sided thyroid lobes were stained with hematoxylin and eosin, PAS, and immunohistochemichal stain for calcitonin Ab-2. Specimens of the left- sided thyroid lobes were stained with toluidine blue for semithin sections. Statistical analysis including the level of T4, the height of follicular epithelium and parafollicular cell, mean area percent of colloid, mean area percent, optical density of calcitonin immunoreaction and number of C-cells were measured in both hypo and hyperthyroid state. The midshaft femur of all groups were prepared and stained with H&E. Cortical bone thickness and diameter of haversian canals were measured morphometrically.Results: in hypothyroid rats both follicular and C-cells displayed signs of hyperactivity. Whereas in hyperthyroid rats, both cells displayed signs of hypoactivity. This was also reflected on the changes observed in bone sections. Regarding the results, there was a statistical significant difference between the two thyroid conditions versus the control group.Conclusions: both hypothyroid and hyperthyroid conditions pointed to a functional interrelation between follicular cells and parafollicular cells of the thyroid gland. Hyperthyroidism increased bone resorption leading to osteoporosis. Hypothyroidism decreased bone resorption resulting in increased cortical bone thickness.