We developed a new treatment, Gamete Intrafallopian Transfer with the preincubated oocyte (New GIFT) and applied this method to all kinds of infertility where the patient had at least one tube. We performed 114 New GIFTs and dealt with the factors which influenced the establishment of pregnancy. 1. The pregnancy rate was 37%/cycles (42/114), 42%/patients (42/100) and the abortion rate was 19% (8/42). These results show that the New GIFT was more efficient than the original GIFT. 2. The most important factor for the establishment of pregnancy among the semen parameters was sperm motility, especially at the time of insemination. The pregnancy rate increased as sperm motility became higher. The sperm count did not influence the pregnancy rate significantly except in severe cases of oligozoospermia. 3. The most important factor in oocyte assessment was the number of mature oocytes. The number of oocytes in the pregnant group was much more than that in the nonpregnant group, but the total number of follicles in the pregnant group was found to be from 3 to 7 follicles. No pregnancy occurred when the number of follicles was greater than 11. These results suggested that existence an optimum number of oocytes. Conditions of the corona-cumulus component complex closely related to the establishment of pregnancy. The pregnancy rate was about 60% when more than 2C (-) oocytes (almost all cumulus cells were dispersed) were transferred, but it was only 5% when only C (+) oocytes (hardly any cumulus cells were dispersed) were transferred. 4. The most effective luteal support regimen was the pill. The administration of progesterone induced a high percentage of abortions.