Abstract 1. 1. Thyroidal iodine, protein and thyroglobulin (TG) were investigated in a hibernator, Spermophilus richardsoni, sampled in the field and from laboratory-held winter colonies. 2. 2. In field animals, thyroidal iodine and protein contents were similar at onset of hibernation and at terminal arousal. 3. 3. Iodine content was increased in laboratory-held animals, a function of alimentary supply, but no differences were observed between hibernators and non-hibernators. 4. 4. Density sucrose gradients showed that approx. 20% of the TG was present as the 12S precursor sub-unit. 5. 5. No variations in the iodine content, nor the iodoamino acid composition of the TG occurred as a function of hibernation.