The purpose of this study was to measure circulating TSH, T ₄ and fT ₄ concentrations in dogs submitted to a clinical visit for general symptoms (weight gain, polyuria and polydipsia, changes in hair coat). Twenty-eight dogs, 14 cross-breed and 14 purebreds (Golden Retriever, Labrador, Doberman), of both sexes (14 males and 14 females), aged 8 to 14 years, were assessed. No significant differences of circulating TSH, T ₄, fT ₄ concentrations between the baseline and after therapeutic treatment nor between intact and neutered females were observed. Compared to baseline values, intact males showed higher TSH concentrations (p0.01), and castrated males lower TSH concentrations (p0.01) after therapeutic treatment. Compared to intact males, castrated males showed baseline TSH concentrations higher (p0.01), but lower (p0.01) after therapeutic treatment. No significant differences of T ₄ and fT ₄ concentrations between baseline conditions and after therapeutic treatment, nor between intact and castrated males, were observed. The experimental sample considered in this study falls within that casuistry involving elevated TSH concentrations but low serum T ₄ and fT ₄ concentrations or close to the minimum physiological cut-off, in which the common clinical signs suggestive of hypothyroidism was, essentially, overweight and neglected appearance of the hair.