The principal aim of the study was to relate ultrasound-derived indices of blood flow in individual follicles on the day of, but before, the administration of human chorionic gonadotrophin (HCG) to the subsequent recovery of oocytes and the production of preimplantation embryos. Data were obtained from 21 women (aged 29-43 years) with bilateral tubal occlusion, who were undergoing treatment by in-vitro fertilization (IVF) and embryo transfer. Transvaginal ultrasonography with colour Doppler imaging and pulsed Doppler spectral analysis were used to measure follicular volume and derive indices of blood flow. The end-points for each follicle were the volume, peak systolic velocity (PSV), pulsatility index (PI), and the recovery or non-recovery of an oocyte, the subsequent production or non-production of a preimplantation embryo and the morphological grade of each embryo. A total of 94 follicles were studied; 74 oocytes were recovered (79%) and 40 embryos (33 grade I or II) were produced. There were four clinical pregnancies (pregnancy rate 25.0% per transfer, 19.0% per patient). There was a significant correlation between whether or not follicular blood flow was detected and whether or not an oocyte was recovered (P < 0.05, chi 2 test). The values for volume and PI were not clinically useful. The PSV (cm/s, mean +/- SD) was higher in follicles that were associated with the production of an embryo (12.7 +/- 5.9) compared with those that were not (8.5 +/- 5.0; P < 0.05, Student's t-test). The probability of producing a grade I or grade II embryo was 75% if the PSV was > or = 10 cm/s. The corresponding value was 40% if the PSV was < 10 cm/s and 24% if blood flow was not detected (i.e. PSV < 3 cm/s). There was a significant increase (P < 0.05, Student's t-test) in the PSV before aspiration in those follicles associated with the subsequent production of an embryo. We conclude that the value for PSV, before the administration of HCG, can be used to identify follicles with a high probability of producing an oocyte and a high grade preimplantation embryo. The information may also be used to time the administration of HCG to achieve the optimum number and quality of embryos for patient management.