In order to define the usefulness of subzonal sperm insertion (SUZI) and intracytoplasmic sperm injection (ICSI), we studied in a comparative trial 46 consecutive treatment cycles of microassisted fertilisation by SUZI and ICSI. By ICSI 9% of the oocytes in metaphase II were damaged in 26 treatment cycles, by SUZI, however, not one single egg in 20 cycles (p < 0.001). Fertilisation rate after ICSI (65%) was, particularly in cases with combined sperm defects as well, significantly higher than after SUZI (35%; p < 0.001). Additionally, after ICSI a higher transfer (100% vs. 75%; p < 0.05) and pregnancy rate could be obtained (38% vs. 10% per cycle; p < or = 0.05). At the moment, 3 healthy children are born (2 after SUZI, 1 after ICSI), 4 patients are in the 2nd and 3rd trimenon, respectively, the remaining 5 patients aborted. In conclusion, the ICSI technique yields better results than SUZI, especially in cases of very severe male subfertility.