The use of luteal phase support has been demonstrated in patients undergoing an IVF/ET procedure. This study was designed to compare the absorption and the efficacy of two different luteal supports: 17-alpha-hydroxyprogesterone caproate (Lentogest, AMSA, Italy) and natural Progesterone (Prontogest, AMSA, Italy). A total of 80 patients received luteal supplementation with 50 mg of natural P/day intramuscularly, until beta-hCG evaluation. Then, in case of positive beta-hCG, patients were randomly divided into two groups (A and B) in order to compare two different protocols: Group A, 17-OHPc (341 mg once a week) and Group B, natural P (50 mg/day) both intramuscularly and extended for 10-12 weeks. Our study showed that the treatment with 17-OHPc results in a higher percentage of pregnancy rate compared to natural P, but the differences are not statistically significant. Thus, we emphasize that 17-OHPc preparation for better acceptance appears to be the most suitable and comfortable method for luteal phase support.