Objective   To investigate the protective effect of ultraviolet blood irradiation and oxygenation (UBIO) on erythrocyte immune function in patients during cardiopulmonary bypass (CPB).    Methods   Sixty-seven patients undergoing elective heart valve replacements with CPB were randomly divided into control group (

n

=34) and experimental group (

n

=33). In experimental group

UBIO accumulated the blood from the subclavian vein (10 ml/kg) was dealt with ultraviolet i

rradiation (wave length 240 to 300 nm) and oxygenation (FiO

2

100%)

and then the ultraviolet-irradiated and oxygenated blood was added into cardiopulmonary-bypass circuit priming while equivalent quantitative saline was added to the control. Peripheral venous blood samples of all patients were collected at following time points

during and after cardiac surgery

after induction of anaesthesia

30 min after start of CPB

24 h and 7 d after surgery

which were anticoagulated with heparin for dynamically detecting the changes of RBC-C3bRR and RBC-ICR. The serum concentration of malondialdehyde (MDA) and activity of superoxide dismutase (SOD) were compared  between the 2 groups before aortic cross-clamping and after aorta declamping.    Results   At the time of aorta declamping in experimental group

MDA was lower but SOD was higher than those of the control. RBC-C3bRR and RBC-ICR in the experimental group were significantly higher at 30 min after beginning of CPB

24 h

and 7 d after operation than those in the control (

P

<

0.05).    Conclusion   UBIO markedly mitigates the impairment of erythrocyte immune function caused by CPB and promotes the recovery of erythrocyte immunity in patients after CPB. This protective effect may be due to the maintenance of structural integrity of red blood cells and the attenuated injury of red blood cells by free radicals.