Objectives: The present study aimed to evaluate changes in serum levels of granulocyte colony stimulating factor (G-CSF) throughout the course of preparation of infertile women assigned for intra-cytoplasmic sperm injection (ICSI) so as to define its role for prediction of oncoming pregnancy. Patients & Methods: The study comprised 70 infertile couples with tubal or male factor infertility. After all the couples completed the standard infertility work-up, females underwent controlled ovarian hyperstimulation. Intramuscular hCG 10,000 IU was administered when at least 5 follicles were ≥18 mm in diameter with adequate serum E2 levels (hCG injection time). Oocytes were retrieved 34–36 h after hCG administration (OR time). Occurrence of pregnancy was assured by β-hCG determination, 16 days after OR. Venous blood samples were obtained prior to (Pre-OS) and at Day-6 after ovarian stimulation, at hCG injection time and at OR time. Follicular fluid was collected during oocyte retreival. Serum and FF levels of G-CSF were ELISA estimated. Results: Patients categorization according to hormonal response (HR) manifested as serum E2 levels showed that 9 females (12.9%) had low, 46 females (65.7%) had moderate and 15 females (21.4%) had high HR. Mean G-CSF serum level showed steady progressive increase throughout the study period reaching a peak at OR time. However, follicular fluid G-CSF level estimated at time of OR was significantly higher compared to its serum level estimated at the same time. Serum levels of G-CSF showed a non-significant difference between patients categorized according to HR up to 6-days of rFSH injection. At time of injection of hCG, serum G-CSF was significantly higher in high (p1