The effects of furosemide, digoxin and thiopental sodium on plasma ANP level were studied in five, six and three children with CHF respectively. The effect of captopril on plasma ANP level was also studied in four hypertensive children. Plasma ANP level showed a significant decrease with the use of furosemide, although it did not change significantly after the administration of digoxin, thiopental sodium and captopril. These findings suggest that the elevated plasma levels of ANP previously reported in congestive heart failure may not result from the pharmacological effects of medicine used for treatment.