The objective of the study was to evaluate, in patients with unexplained infertilty, the possible relationship between anticardiolipin antibodies and indices of uterine artery Doppler measurements. A total of 46 infertile women participated in the study and underwent ovarian stimulation. Transvaginal ultrasonography and colour Doppler were performed on the day of embryo transfer and patients were divided on the basis of pulsatility index (PI): group I, PI <2.5; group II, PI 2.5-3.0; and group III, PI >3.0. On the same day that Doppler analysis took place, peripheral blood was obtained and circulating anticardiolipin antibodies were assayed. The response to ovarian stimulation was similar in the three studied groups. No significant differences in oestradiol and ultrasonographic parameters were observed between the groups. A significant increase in anticardiolipin antibodies was observed in those patients with higher resistance to flow at the level of the uterine artery. A significant relationship was found between the uterine artery PI and anticardiolipin immunoglobulin G class (F = 14.35; P = 0.001), and immunoglobulin M class (F = 5.88; P = 0.020). It is concluded that, in unexplained infertility, anticardiolipin antibodies may be involved in uterine vascular modifications and that Doppler flow analysis of uterine arteries may be an important tool in the assessment and management of ovarian stimulation.