The aim of this study was to evaluate the relationship between uteroplacental circulatory insufficiency and the maternal release of adenosine in pregnancies complicated by toxemia. Uterine artery Doppler velocimetry was performed immediately before maternal arterial blood sampling in 16 pregnant women complicated by toxemia and 6 normal pregnant women. Maternal arterial blood was then analyzed for plasma adenosine levels. The mean maternal arterial plasma adenosine level in pregnant women complicated by toxemia was 0.85±0.18 μmol/L, significantly higher than in normal pregnant women 0.54±0.12 μmol/L. Furthermore, the evaluation of plasma adenosine levels was related to the presence of a protodiastolic notch in the uterine artery waveform. The results suggest that increased maternal adenosine levels are associated with placental blood flow in pregnancies complicated by toxemia.