BACKGROUND: Peritoneal fluid (PF) analysis is a valuable diagnostic tool in equine medicine. Markers such as serum amyloid A (SAA) and haptoglobin (Hp) could facilitate the diagnosis of inflammatory abdominal conditions. OBJECTIVES: The objectives were to (1) establish reference intervals (RI) for SAA and Hp in serum and PF in healthy horses, (2) compare SAA and Hp concentrations between healthy horses and horses with colic, and (3) to assess the correlation between serum and PF concentrations. METHODS: Serum amyloid A and Hp concentrations were determined by automated assays in prospectively enrolled healthy reference horses and horses with colic. RIs were calculated, group concentrations were compared by Student's t-test, and Pearson's correlation for serum and PF concentrations were determined. RESULTS: In healthy horses (n = 62) the measurements for SAA were below the detection limit (0.5 mg/L) in 94% of serum samples and 98% of PF samples. Horses with colic (n = 61) had statistically significantly increased SAA concentrations in serum (P