The purpose of this study was to identify prognostic indicators that may help to predict outcome in clinical cases of diffuse peritonitis treated with open peritoneal drainage. Medical records from 19 canine patients with generalized peritonitis treated with open peritoneal drainage between 1990 and 1996 were reviewed. The signalment, preoperative complete blood count (CBC), preoperative biochemical profiles, and number of days of open peritoneal drainage of surviving patients (n = 15) were compared to nonsurviving patients (n = 4). Significant differences were noted between the surviving and nonsurviving groups in the ALT (p = 0.02) and GGT (p = 0.01) values. Seventy-nine percent of the patients in this study survived.