The associations between Doppler ultrasound-derived luteal blood flow indices and luteal hormonal profile in the midluteal phase were assessed in both spontaneous and stimulated cycles. Transvaginal color Doppler ultrasound evaluation and blood sampling were carried out prospectively on 61 infertility patients in 43 spontaneous cycles, 31 clomiphene citrate (CC) cycles, and 16 controlled ovarian hyperstimulation (COH) cycles in the midluteal phase. Luteal blood flow Doppler indices included peak systolic veloicty (PSV), time-averaged maximum velocity (TAMXV), pulsatile index (PI), and resistance index (RI). Hormonal profile indices included serum levels of 17 β-estradiol (E2), progesterone (P) and P/E2 ratio. The correlation between each end-point in each treatment group was assessed by regression analysis. PSV and TAMXV in the COH group were significantly higher than in the spontaneous group (P=0.0435 vsP=0.0359, respectively). Serum E2 and P were significantly higher than in the spontaneous group (P=0.0435 vsP=0.0359, respectively). Serum E2 and P levels were significantly higher in the COH group than in the CC (P<0.0001 vsP<0.0001, respectively) and spontaneous groups (P<0.0001 vsP<0.0001, respectively). PSV and TAMXV correlated positively with P level in spontaneous cycles (P=0.0131 vsP=0.0142, respectively) and CC (P=0.0120 vsP=0.0066, respectively) but correlated negatively P level in COH cycles (P=0.0348 vsP=0.0383, respectively). PI and RI correlated with P only in CC cycles (P=0.0357 vsP=0.0369, respectively). Doppler ultrasound-derived indices all correlated with P/E2 ratio in spontaneous and CC cycles but not in COH cycles. These results indicate that velocity indices should be considered as complementary parameters of luteal function for infertility but that the relationship of these indices to P level in COH cycles differs from that in spontaneous and CC cycles. The correlation of luteal blood flow indices with P/E2 ratio suggests that Doppler ultrasound indices may be useful in predicting reproductive outcome in spontaneous and CC cycles.