Purpose: To corroborate or refute a previous study suggesting that intrauterine infusion of granulocyte colony stimulating factor (GCSF) could significantly improve endometrial thickness into more fertile levels when the endometrial thickness was ≤ five mm. Materials and Methods: Three women whose endometrial thickness never exceeded five mm on the in vitro fertilization-embryo transfer(IVF-ET) cycle or subsequent attempted frozen ETs using graduated estradiol had intrauterine infusion of G-CSF to the estradiol regimen. Results: Not one of the three women improved the endometrial thickness beyond five mm and none conceived on the G-CSF cycle. One woman had a subsequent pregnancy following a frozen ET with only a four-mm thickness with no infusion of G-CSF. Conclusions: These data do not confirm the efficacy of intrauterine infusion of G-CSF for poor endometrial thickness. Perhaps only certain cases will respond. A larger series could take time to accumulate since other studies have shown that only 0.3% of women with ≤ five mm endometrial thickness in the late proliferative phase during an IVF-ET cycle will not improve the endometrial thickness > five mm using graduated estradiol protocols.