Serum and abdominal fluid concentrations of 12 substances were evaluated in groups of dogs who had ischemic obstruction, simple intestinal obstruction, or sham operation performed. One group was used as a control model. No significant changes were found in serum. In abdominal fluid, the following changes were noted: lactic dehydrogenase increased from 18.3 to 136.9 units/ml (simple obstruction group), and from 18.2 to 228.7 units/ml (ischemic obstruction). Aldolase rose from 4.13 to 13.62 units/ml (simple obstruction), and from 1.99 to 16.28 units/ml (ischemic obstruction). Intestinal alkaline phosphatase rose from 0.11 to 0.89 units/ml. There was a significant increase in both the control group and the simple obstruction group after 3½ hours. Lactic acid rose from 0.226μM/ml to 1.636μM in the ischemic group.