Karen Purcell's book _ Essentials of Ferrets..._ is the most recent reference and she writes that "Thyroid disorders are uncommon in the ferret ... There are anecdotal reports of hypothyroidism...". She goes on to mention thyroiditis in conjunction with Aleutian Disease, and two cases of thyroid adenocarcinoma, referring back to Fox's book for both of them. Thyroid values are in her text on page 151. Karen Rosenthal had not at the point where she wrote chapter 10 of _Ferrets, Rabbits and Rodents..._ encountered any articles on thyroid problems in ferrets and had not run into a case of either in ferrets. This Hillyer and Quesenberry text (F, R., and R..._) gives mean levels per genders in Table 9.1 on page 88. In Fox's most recent text the mention in relation to Aleutian was from unpublished observations in 1986. In the case of thyroid involvement in adenocarcinoma there was a survey of 4,774 ferrets, with a total of 639 tumors of assorted types, and only ONE was of this type and location but clinical data on that ferret was not available ( Li, Fox, Padrid, "Neoplastic Diseases in Ferrets, 574 Cases" (1968 - 1997) JAVMA 1998; 212:1402). A second case later appeared in a zoo male presenting with dysphagia (problems swallowing) with the clinical signs being weight loss and a thin coat for two years, and the ferret had first been tried with a diet change which helped on both scores until he was one day found semi-conscious a year later. He did not survive corrective surgery which was attempted at that point, and he had further illnesses present (chronic respiratory disease, insulinomae, and bilateral adrenal hyperplasia) on necropsy. You will find a photo of the very large throat lump seen when he was shaved, and radiograph in _Biology and Diseases of the Ferret_. Thyroid values are given on page 137 of Fox's book, and further information on other aspects else in the text. I seem to recall Bruce Williams once mentioning that while he knew of a very few hyperthyroid cases that hypothyroid in ferrets was not seen by him. That's from memory and could be wrong. It was from back when a few people were actively pushing that hypothyroidism was in their ferrets but when push came to shove they wouldn't test the thyroid values or didn't report the results when they finally did test. While thyroid problems certainly can happen my own personal inclination at this level in the information matrix is that a number of people take the human tendency toward such difficulties and try to project that onto ferrets. If more testing were done they might be proven right but right now the current results do not back that hypothesis and until these people put their money where their mouths are by actually testing and then making sure that the results get to publishing researchers through vet-to-vet contacts there will be no hard data supporting their premise. It may be that such testing is actually underway somewhere now or that there are some individual very interesting cases lying away in files; without communication and publications of hard data the suppositions remain only that. [Posted in FML issue 2818]