Residence time of purified human BChE in mice 0.2 ml of purified native human BChE containing 438 units was injected i.p. into 5 mice, at a dose of 27 mg/kg. Blood samples were collected at 0, 1, 2, 4, 6, 8, 10, 24, 34, 48, 72, 96, 168, and 216 hours and assayed for BChE activity. At time zero the BChE activity in mouse blood was 1.79±0.16 u/ml. The mean residence time was 56.6 hours.