In this study plasma concentrations of IL-1α and IL-8 in 29 female dogs with malignant mammary gland tumours (19 without metastasis and 10 with metastasis) and in 10 healthy control animals were determined. Concentrations of IL-1α and IL-8 were analysed using a specific canine ELISA assay. Mean plasma concentrations of IL-1α and IL-8 were significantly higher (p<0.05) in female dogs with both non-metastatic and metastatic malignant tumours compared to the healthy animals. The concentrations of both tested cytokines were significantly increased (p<0.05) in the dogs with metastasis. In female dogs with mammary carcinomas, the plasma concentration of IL-1α was significantly higher (p<0.05) in the animals with grade 3 tumours compared to the dogs with grade 1 tumours. The concentration of IL-8 was significantly higher (p<0.05) in the dogs with grade 3 tumours compared to that found in the animals with grade 1 and grade 2 tumours. A moderate correlation (r=0.433) was found between IL-1α and IL-8 concentrations in the female dogs. These findings suggest that increased malignancy and invasiveness of canine mammary tumours is associated with an increased production of IL-1α and IL-8 in the tumour microenvironment, which, in turn, leads to an increase in their circulating levels. This may indicate that circulating levels of the cytokines investigated could be considered as diagnostic and prognostic markers in canine malignant mammary tumours. However, further studies in this fields are needed