CGRP, which coexists with acetylcholine in trigeminal motoneurons, could be one of the regulatory anterograde factors responsible for the enhanced expression of AChR subunits in neuromuscular junction. It has been also shown that low level of thyroid hormone plasma concentration has influence on the transitional development of muscle fibers and related motoneurons through a sever reduction in AChR density. Up today, no previous study has shown specific alteration of CGRP component of motoneurons in developing hypothyroid life. To this purpose, the chemical hypothyroid weaned pups (a %50 reduction in weight gain) were processed for immunohistochemistry, a semiquantitative evaluation was carried out to estimate the proportion of strongly, intermediately, and weakly labeled trigeminal motoneurons, as well as those totally lacking CGRP staining. Hypothyroid pups show a significant reduction in the number of strongly and intermediately CGRP reactive Vth motoneurons (%20 + %36 respectively), notably two times more unlabelled neurons were observed in normal weaned pups. On our preliminary observation on soma size, a three times increase in the number of small CGRP motoreurons reached to a three times decrease in large motoneurons existence. Certainly these obvious alterations emerging from direct or indirect thyroid hormone deficiency on both motoneuronal and muscular relation might be of physiological importance for a potential masticatory system during suckling period of nutrition and growth.