Randomized, partially blinded. Infants were assigned to deep hypothermia and either circulatory arrest or low-flow bypass support during arterial switch surgical repair of transposition of the great arteries. Randomization was stratified by diagnosis (with or without septal defect) and by specific surgeon of three, thus yielding six strata within each treatment group. Randomization was also blocked to minimize imbalances in treatment assignment between strata. The study was partially blinded, in that outcome data were obtained by investigators who were unaware of management, surgical care, and intensive care were standardized. Hemodynamic assessment was made early in the post-operative period. The outcomes of primary interest (magnetic resonance imaging, neurologic examination, and psychometric testing) were reviewed at the one-year evaluation, to maximize relevance to the long-term prognosis. Pre-operative and seven-to-ten day post-operative neurologic examination was also carried out. Developmental status at one year was measured by the Bayley developmental scales and the Fagan test of infant intelligence. Brain function was assessed by neurologic examination at one year. The recruitment period extended from April 1988 to February 1992.