This study aimed to evaluate the physiological, haematological and biochemical changes during a treadmill incremental exercise test (IET). Animals were submitted to five stages of 6 min each, at 6, 7, 8, 9 and 10 mph, at an inclination of 5%. Blood samples were collected at rest (T0), immediately after exercise (T5) and after a 20 min rest period (T6), to determine complete blood count, urea, creatinine, creatine kinase, aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, total plasma protein, albumin, alkaline phosphatase (AP), cholesterol, triglycerides (Trig), Ca2+, Na+, K+ and Cl-. Blood lactate (BL), heart rate (HR), rectal temperature (RT) and glycaemia were measured at rest (T0), after each stage (T1-T5) and after the rest period (T6). Variations were recorded between T0 and T5 in red blood cells, haemoglobin, AP, Na+, K+ (P<0.01), Trig (P<0.05), Ca2+ and Cl- (P<0.02). Differences were observed in BL at T5 (P<0.02) and T6 (P<0.02), RT at T2-T6 (P<0.01), HR at T3-T5 (P<0.01) and glycaemia at T2-T4 (P<0.01) and T5 (P<0.05). This study is a novel description of the shifts of physical fit police working dogs during this IET protocol.