The effectiveness of urokinase therapy for thrombosis in children, par
ticularly in newborn infants, has not been established. We report our
experience with the local administration of high-dose intrathrombus ur
okinase in two newborn infants. One infant had aortic thrombosis and t
he other, thrombosis of the right femoral artery. The known abnormalit
ies in the newborn's fibrinolytic mechanism provide the rational basis
for the therapeutic use of high doses of plasminogen activators. No s
ignificant abnormalities of our patients' fibrinolytic systems were fo
und, and effective thrombolysis was achieved. A literature review of t
he use of urokinase therapy for thrombosis in children reveals great d
isparities in dosage and outcome. We believe that fixed-dose regimens
should be replaced by individually adjusted thrombolytic therapy and t
hat the need for higher doses of urokinase in newborns should be studi
ed further.