The aim of this study was to measure serum neopterin and C-reactive protein (CRP) concen- trations in female dogs with mammary tumours and evaluate the association between the values of these indicators and some clinical characteristics of the tumour. Fifty three female dogs were used for this study, including 43 dogs with mammary gland tumours (10 benign and 33 malignant) and 10 healthy controls. The concentrations of neopterin and CRP were determined using the ELISA technique and commercial ELISA kits. The mean serum neopterin concentration in fe- male dogs with mammary tumours was lower than in healthy dogs, but significant difference was not found. Similarly, there were no significant differences in neopterin concentrations in female dogs based on tumour size, tumour ulceration and metastasis. The mean CRP concentration was significantly higher (p<0.05) in dogs with malignant tumours compared to dogs with benign tu- mours and control. Furthermore, serum CRP concentration was significantly higher (p<0.05) in dogs with metastatic malignant tumours compared to dogs with non-metastatic mammary tu- mours. The CRP concentration was significantly lower (p<0.05) in dogs with tumours less than 3 cm compared to those with larger tumours, and significantly higher in dogs with ulcerated tu- mours compared to those without ulceration. Our findings suggest that the neoplastic process in the mammary gland does not cause significant changes in serum neopterin concentrations in dogs. Higher concentrations of serum CRP in dogs with advanced stages of malignant tumours may suggest that CRP could be a potential prognostic marker in canine malignant mammary tu- mours, but this hypothesis needs further study.