Objective: To determine whether varied human spermatozoa detected also with monoclonal antibodies against acrosomal proteins, have an influence on fertilization, transfer, pregnancy and implantation rates using ICSI. Design: A retrospective study. Setting: A private IVF center and academic research laboratory. Patients: 1240 men participating in the ICSI program. Interventions: Sperm were divided into seven groups: oligozoospermia, oligoasthenozoospermia, ligoasthenoteratozoospermia, fresh and frozen/thawed epididymal and fresh and frozen/thawed testicular sperm. Fertilization, transfer, pregnancy and implantation rates were recorded in each category. Sperm were tested with antibodies for detection of the of the sperm acrosome. Main outcome measure: Fertilization, transfer, pregnancy and implantation rates, percentage of acrosome-reacted cells. Results: The fertilization rate and statistical evaluation showed differences between morphologically normal and pathological sperm and other groups. The freezing-thawing procedure had no influence on the fertilization of testicular sperm but epididymal frozen/thawed sperm had a higher fertilization rate. Immunofluorescence proved decreasing sperm quality in all groups compared to the control group. This difference is not manifested in other parameters (transfer, pregnancy, implantation rates). Conclusion(s): The spermatozoa with varied semen characteristics and good quality, also detected with specific antibodies, gave the best fertilization rates. The paternal effect is not proved in other parameters.