Thyroid hormones regulate a variety of physiologic functions including metabolism, growth, and reproductive cycling, and these other hormones can impact the thyroid function via the hypothalamic–pituitary axis. For instance, the gonadotropin-releasing hormone agonist, deslorelin, used in nondomestic carnivores for contraception and behavioral control, down-regulates reproductive hormones through this mechanism and so may impact thyroid function. Due to clinical concerns of hypothyroidism in a bachelor group of adult male Pallas' cats (Otocolobus (Felis) manul) which also had deslorelin implants, serum samples from treated captive (n = 8) individuals, untreated captive (n = 25), and free-ranging (n = 9) individuals were analyzed for thyroid hormone concentrations. Total and free thyroxine (TT4 and FT4), total and free tri-iodothyronine (TT3 and FT3), and thyroid stimulating hormone (TSH) were measured although, due to sample volume limitations, not every hormone could be analyzed for every sample. Of these hormones, only FT4 was found statistically different between the deslorelin-treated and untreated groups. As samples were unevenly distributed across season, true comparison between seasons could not be made. The values reported for the untreated captive and free-ranging group, while representing a small sample size, can serve as a baseline assessment when evaluating the thyroid status of captive Pallas' cats.