&NA;Metabolic changes between the preoperative period and the defunctionalized stage after ileal pouch‐anal anastomosis were investigated in 21 patients. Aspects studied included weight change, renal function, liver function, lipid metabolism, and two hematologic parameters. Of 21 patients, 19 lost weight. Cholesterol levels decreased from 183±30 IU/I to 122±48 IU/I (P<.0001). Triglyceride levels rose from 95±29 IU/I to 190±86 IU/I (P<.01). Significant elevations were seen in values of four liver function tests: SGOT, SGPT, lactic dehydrogenase, and alkaline phosphatase (P<.05). Blood urea nitrogen levels increased from 11.1±4.7 mg/100 ml to 21.8±24.8 mg/100 ml (P<.05). Serum creatinine levels rose from 0.97±.18 mg/100 ml to 1.5±1.2 mg/100 ml (P<.05). Uric acid levels increased from 5.6±1.8 mg/100 ml to 7.5±2.3 mg/100 ml (P<.001). Hemoglobin values did not change significantly. Platelet counts rose from 304,000±79,000 to 447,800±189,000 (P<.05). Identification of these systematic alterations in metabolic parameters during the defunctionalized stage can aid the physician in management of these patients.