To evaluate the effect of three different modes of luteal support: only progesterone (P), P with 6 mg oral estradiol (E2) valerate and P with 6 mg vaginal E2 valerate on luteal serum E2 levels and patterns and pregnancy rates in women undergoing intracytoplasmic sperm {ICSI} cycles, using the long agonist protocol. Prospective randomized study. 270 infertile patients who were candidate for ICSI cycles, for first time, due to male factor infertility were prospectively included in the study. All participants should have more than 5 mature oocytes at retrieval and at least one good quality embryo available for transfer. In all patients, the long luteal down-regulation protocol was used. From the day of embryo transfer, patients were prospectively randomized to receive either, only P (group A, n = 90), P with 6 mg oral E2 valerate (group B, n = 90) or P with 6 mg vaginal E2 valerate {placed in upper third of vagina}(group C, n = 90) for luteal support. - Luteal E2 and P profiles on days 0 (day of hCG), 7, 10 as well as day 13. Luteal E2 and P levels of the 3 groups were considered together on days 0, 7 and 10. Whereas, on day 13 non-pregnant cases were compared separately in order to rule out the influence of early levels of hCG. Clinical pregnancy rate was documented. Day 0 E2 levels were similar in the 3 groups. Group A had significantly lower E2 levels on days 7, 10 and 13 and a higher magnitude of E2 decline on days 7 and 10 in comparison with those in groups B & C. Similar levels of luteal E2 were documented in groups B and C. Luteal serum P levels were similar in the three groups. The highest pregnancy rate was achieved in group C (45.56%), however, only the difference between group C and A was found to be statistically significant (P=0.031). In addition, a significantly higher early spontaneous abortion rate (ESA) was observed when comparing group A (22.2%) with either group B (3.03%, P=0.002) or group C (2.44%, P=0.035), while, no significant difference was found when comparing group B with group C . Statistical analysis As the data are normally distributed, continuous variables are expressed as mean ±SD. Statistical comparisons were carried out by ANOVA, Chi-square test, Fisher's Exact test or Student's t-test, as indicated. P<0.05 was taken as statistically significant. For patients who are treated with the long agonist protocol, the addition of 6 mg vaginal E2 valerate to P supplementation regimen appears to enhance the probability of pregnancy.