We used power Doppler imaging to examine neovascularization in the corpus luteum (CL) in 12 healthy volunteers. We also investigated whether CL blood flow reflected luteal function. The ratio of the area of vessels in the CL to the area of a sectional plane at the maximum diameter of the CL observed by power Doppler (FA ratio) was used as a quantitative index of the vascularity of the CL. The pulsatility index (PI) was significantly lower in ovarian arteries with CL than without CL (P < 0.05). Changes in ovarian arterial and intra-luteal PI appeared to reflect physiological changes in the vasculature of the CL. There was no correlation between the volume of the CL or the FA ratio and the concentration of progesterone. The pattern of changes in the product of the FA ratio and the CL volume and in the progesterone concentration was similar. The progesterone concentration was positively correlated with this product (r = 0.74, P < 0.01). The product of the FA ratio and the CL volume plateaued during the mid- to late luteal phase, suggesting the presence of functional and structural luteolysis. These findings suggest that colour Doppler ultrasonography, including power Doppler imaging, can detect physiological changes in the blood flow of the ovary in the luteal phase, and may be a useful noninvasive tool for evaluating CL function.