The acute phase proteins (APP) form part of a non‐specific host response to inflammation. They may be induced by a range of different causes, including infection, inflammation, cancer and trauma. As they form part of the earliest response to such insults, they have potential for early identification of disease. In people, APP levels have been shown to correlate both with the extent of disease and also the prognosis in several forms of neoplasia, including prostate, oesophageal and colorectal cancer. As such, they can be used as prognostic and monitoring tools. To date, similar studies in veterinary patients have been limited, largely retrospective in nature and many are non‐specific for tumour type. The purpose of this study was to evaluate a panel of four APPs in dogs with naturally occurring mast cell tumours (MCTs) and sarcomas to identify in the first instance whether increased levels of individual APPs, or identifiable combinations of APPs, was linked with the presence of disease. In the patients with MCTs, C‐reactive protein (CRP) and α‐1 acid glycoprotein levels increased, with a concurrent drop in serum amyloid A levels. In the sarcoma patients, CRP, α‐1 acid glycoprotein and haptoglobin were increased. These findings suggest that specific solid tumour types in dogs may be associated with specific changes in APP profiles.