The beneficial effect of glucose and phosphate ions in culture medium on the development of human embryos in vitro has not been fully elucidated. The purpose of this study was to evaluate the influence of fertilization and culture of embryos in glucose/phosphate-free m-TALP medium on pregnancy rates in IVF-ET program. The patients in 244 IVF-ET cycles received GnRH agonist + HMG regimens. A does of 10,000 IU HCG was administered when two or more dominent follicles reached 18mm in diameter. Thirty-six hours after HCG, oocytes were recovered transvaginally using ultrasound guidance. Aspirated oocytes were matured for 4 to 6 h in TCM-199 supplemented with 10% follicular fluid (FF). Insemination was carried out with 50,000 motile spermatozoa in TCM-199 + 10% FF or m-TALP + 5% FF + 5% fetal cord serum (FCS) according to experimental design. After 6 h, oocytes were washed 3 to 4 times and cultured in each fresh medium. After 20 h, oocytes were freed from cumulus/corona cells and examined for the presence of pronuclei. Fertilized oocytes were transferred into each co-culture drops and cultured for further incubation. On day 3, embryo transfer was performed with grade 1 and 2 embryos. Monolayers for co-culture of embryos were prepared by plating 1x10(5) cumulus cells/ml in 10 ul drop of TCM-199 + 10% FF or m-TALP + 5% FF + 5% FCS media 24 h prior to the onset of co-culture. Development to 4 to 16 cell stage was observed at 70x magnification following two days of incubation. Pregnancy was confirmed by detecting increasing serum beta-hCG concentrations for 11 days following embryo transfer. Data were analyzed by chi2-test. Oocytes from 244 IVF-ET cycles were randomized. The number of cycles and mean age of patients were 97 and 147, 31.3 yrs and 31.2 yrs for TCM-199 (control) and m-TALP groups, respectively. The mean number of retrieved oocytes/cycle, fertilization rates, number of embryos transferred/ET and pregnancy rates were 11.1 and 10.3, 65.1% and 67.3%, 4.1 and 4.7, 28.9% and 43.8% for TCM-199 and m-TALP groups, respectively. Differences in the pregnancy rates were found between control and m-TALP groups (p<0.05). The pregnancy rate of patients divided according to maternal age groups of < or =30, 31-35, 36< or = were 44.4% and 49.0%, 26.1% and 41.3%,29.2% and 41.2% for control and m-TALP groups, respectively. These data indicate that culture of human embryos in glucose/phosphate-free m-TALP medium improves pregnancy rates.