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The anti-Müllerian hormone (AMH), known as an important factor in reproductive differentiation, has become a widely used diagnostic marker in the field of assisted reproduction in recent decades. Its increasing importance in small animal practice is explained by its presence in the blood in the postnatal period. In males, it is exclusively produced by Sertoli cells of the testis and in females only by granulosa cells of smaller follicles. Therefore, its determination in the blood is used to differentiate intact from castrated/spayed animals and can also help in the diagnosis of cryptorchidism, ovarian remnant syndrome (ORS), ovarian lesions, Sertoli and granulosa cell tumours, as well as being a fertility marker. There are slightly different results in the literature about serum AMH levels in dogs due to differences in experimental designs and hormone assays used in these studies. During my work, I collected blood samples from healthy, reproductively mature female and male dogs presented to the Obstetrics Clinic for routine spay and neuter, and from male and female dogs undergoing surgery for gonadal abnormalities. Blood samples taken immediately before surgery(day 0) and on days 3, 7, 14 and 28 after surgery were analyzed for serum AMH concentrations by a chemiluminescence immunoassay (CLIA) validated for dogs (at the same time as our study), and data were statistically evaluated. In addition to macroscopic examination of the removed gonads, histopathological evaluation of testicular tumours and ORS was also performed. Out of a total of 15 female dogs of different breeds, aged 1.3-14.5 years, 12 dogs underwent routine neutering and 3 animals underwent surgical treatment for ORS. Among the 14 males of different breeds, aged 1-13 years that were sampled, 7 had normal gonads, 3 had testicular tumours and 4 had unilateral abdominal cryptorchid testes. Initial serum AMH differed significantly (P<0.05) between groups created according to sex and gonadal lesions, and we observed a continuous decrease in mean AMH concentrations during the postoperative period in all groups. Serum levels in bitches decreased to baseline by day 14, whereas the significantly higher baseline levels in healthy male dogs reached baseline only by days 21-28. We determined serum AMH half-life in each group and the limit values at each time point to separate neutered and intact animals (healthy or with gonadal abnormality). The results of our study will help veterinarians to correctly evaluate the hormone level values obtained using a measurement method that they can apply more widely in various clinically important instances such as diagnosing gonadal disorders. In the case of an ORS or testicular abnormality, it also helps to define how many days after surgery can complete removal be confirmed by a repeat AMH measurement, and in the latter case, when should metastasis be considered.