[en] Thyroid hormones are thought to be necessary for the utilization of hypophyseal and gonadal hormones apart from their normal functions related to basal metabolism and growth. The environmental stress also exerts pronounced effect on the biochemical characteristics of blood and hormonal response particularly in thyroid gland which are necessary for physiological adjustment. The present experiment was undertaken to study the levels of serum thyroid hormones in relation to age, sex and diurnal variation indigenous goats to Assam