The diffuse inflammation produced by cardiopulmonary bypass might disrupt the blood-brain barrier and lead to the transient neurologic dysfunction occasionally seen after cardiac operations. To evaluate this possibility, blood-brain barrier integrity was measured by carbon 14-aminoisobutyric acid tracer technique after 2 hours of cardiopulmonary bypass in piglets. Six animals were cooled to 28 degrees C on cardiopulmonary bypass and then rewarmed to 38 degrees C before carbon 14-aminosisobutyric acid was injected intraarterially. A control group of six animals underwent median sternotomy and heparinization but were not placed on cardiopulmonary bypass. Blood-to-brain transfer coefficients for carbon 14-aminosisobutyric acid were calculated for multiple brain regions; higher coefficients reflect greater flux of carbon 14-aminosisobutyric acid and suggest loss of blood-brain barrier integrity. The brain regions examined and their transfer coefficients (cardiopulmonary bypass versus control mean +/- standard error of the mean ml/gm/min) were middle cerebral artery territory cortex (0.0032 +/- 0.0002 versus 0.0030 +/- 0.0002; p = 0.42), diencephalon (0.0031 +/- 0.0003 versus 0.0029 +/- 0.0002; p = 0.50), midbrain (0.0028 +/- 0.0002 versus 0.0027 +/- 0.0002; p = 0.86), cerebellum (0.0036 +/- 0.0003 versus 0.0029 +/- 0.0002; p = 0.22), and spinal cord (0.0035 +/- 0.0003 versus 0.0041 +/- 0.0008; p = 0.48). There were no significant differences in transfer coefficients between animals placed on cardiopulmonary bypass and control animals in any brain region examined. The pituitary gland lacks a blood-brain barrier and had a correspondingly high coefficient in control animals and those undergoing cardiopulmonary bypass (0.077 +/- 0.012 versus 0.048 +/- 0.008; p = 0.07). Two hours of moderately hypothermic cardiopulmonary bypass does not disrupt the blood-brain barrier.