The feasibility of studying ovarian arterial blood flow has been demonstrated, using an ultrasonic method combining real-time imaging and pulsed Doppler (the 'duplex' method). Results using a percutaneous full-bladder technique were validated by comparison with use of an ultrasound probe applied directly to the arteries at laparotomy. The ovarian arteries demonstrated qualitatively and quantitatively distinct flow patterns compared with the internal and external iliac arteries. From recorded waveforms a pulsatility index (PI) reflecting vascular impedance was calculated. The PI was found to be lower, indicating increased blood flow, in the artery supplying the ovary carrying the dominant follicle or corpus luteum. Serial studies suggest that this change occurs at an early stage of the menstrual cycle, possibly before the dominant follicle can be recognized by its size or increased hormone production. Uterine arterial flow was also detectable, more accurately abdominally than vaginally, and the changes typical of late pregnancy were already found to be present, though to a lesser degree, in the first trimester.