We studied the alpha- and beta-adrenoceptor activity and catecholamine and cAMP levels in 112 children and infants admitted to the hospital for diagnostic or interventional catheterization of tetralogy of Fallot, ventricular septal defects with or without hypertension, pulmonary stenosis, coarctation of the aorta, and various complex cyanotic congenital cardiac diseases and compared them with 14 children undergoing transcatheter occlusion of patent ductus arteriosus with insignificant left-to-right-shunts. The mean total platelet alpha-adrenoceptor density of the study population was elevated by 73%. Both the increases in acyanotic (p < 0.05) and cyanotic (p < 0.005) patients as well as the difference between the two groups (p < 0.01) were significant. Based on the congenital disease classification, the elevation in receptor density was also significant in all groups of patients, except coarctation of the aorta. On the other hand, the mean lymphocyte beta-adrenoceptor density was attenuated by 27%, showing significant difference between the acyanotic and the patent ductus arteriosus groups, but none between acyanotic and cyanotic or cyanotic and the patent ductus arteriosus groups. Among the congenital groups, only the left-to-right shunts and the pulmonary stenosis group showed significant (p < 0.05) decrease in beta-adrenoceptor density, whereas the affinity of all the groups toward [125I]iodocyanopindolol was hardly influenced. The plasma levels of all three catecholamines, norepinephrine, epinephrine, and dopamine, were elevated, but cAMP remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)