The initial inflammatory stages of the colic syndrome include changes known as acute phase response. The aim of this study was to contribute with the establishment of reference values concerning the electrophoretogram of peritoneal liquid from healthy horses and horses submitted to experimentally induced intestinal obstruction. Twenty-one horses were allotted in four groups: duodenal obstruction (DG), ileum obstruction (IG), left-dorsal colon obstruction (MG), and control group (CG). Peritoneal liquid was sampled before obtruction (T0), with 3 hours of obstruction (T3) and 6, 30, 102 and 174 hours after desobstructing (T6, T30, T102 and T174, respectively). Total protein levels were determined by the biuret method and protein fractions were obtained by SDS-PAGE electrophoresis. The acute phase proteins (APP) identified were Immunoglobulin-A, ceruloplasmin, transferrin, albumin, α1-antitrypsin, heavy and light chains of immunoglobulin-G, haptoglobin, α1-acid glycoprotein and a still unnamed protein, which was called P24. There was no difference (P>0.3) in protein levels among groups, although a significant difference (P>0.05) was observed between distinct experimental moments in each group evidencing a higher response of the APP in the obstructed groups. The APP fractioning of the peritoneal liquid was standardized to establish a standard curve for healthy equines and those submitted to induced intestinal obstruction. Moreover, it was verified that the SDS-PAGE electrophoresis was sensitive and effective to help diagnose abdominal inflammatory processes.