Gamete intrafallopian transfer (GIFT) was used to treat 32 couples where the male partner was oligospermic (less than 12 X 10(6) motile spermatozoa per milliliter of semen). Initially, 100,000 motile spermatozoa were transferred per fallopian tube and no pregnancies were achieved in 11 cases. The technique was then modified so that a maximal number of motile spermatozoa were transferred (range, 0.11 to 0.90 X 10(6) spermatozoa) and 6 of 21 (29%) pregnancies resulted, with 325,000 spermatozoa being the lowest number associated with pregnancy. It appears that the modified GIFT technique, whereby an increased number of motile spermatozoa are replaced with the oocytes, is an effective therapy in the treatment of oligospermic infertility.