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We examined the changes in circulating choline status in humans in response to major surgery by measuring serum free and phospholoipid-bound choline concentrations before, during and 1-72 h after total abdominal hysterectomy, off-pump coronary artery graft surgery or brain tumor surgery. Preoperatively, the mean serum free and phospholipid-bound choline concentrations in patients scheduled for abdominal hysterectomy (n = 26), off-pump coronary artery grafting surgery (n = 34) or brain tumor surgery (n = 24) were 12.3±0.5, 12.1±0.4 and 11.4±0.4 μmol/l, and 2495±75, 2590±115 and 2625±80 μmol/l, respectively. Serum free choline and phospholipid-bound choline concentrations decreased from these baseline values to 8.8±0.7 (p<0.001), 8.8±0.5 (p<0.001) and 8.2±0.4 μmol/l (p<0.001), and 2050±108 (p<0.001), 2166±59 (p<0.001) and 1884±104 μmol/l (p<0.001) at 1 h after hysterectomy, off-pump bypass graft surgery or brain tumor surgery, respectively. They remained at these low levels for 24 h and then gradually increased towards the preoperative values at 48–72 h postoperatively. Serum cortisol increased postoperatively in all surgical patients for 24 h and its levels were inversely correlated with serum free and bound choline concentrations. These results show that circulating free and bound choline concentrations decrease for 72 h after total abdominal hysterectomy, off-pump coronary artery graft surgery or brain tumor surgery in humans.