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Fertilization abnormalities (premature chromosome condensation of spermatozoa (PCC), triploidy, haploidy) were analysed in order to determine their origin. PCC occurs in 9% of unfertilized oocytes and seems to be the consequence of a failure of oocyte activation, leading to the continuing presence of cytoplasmic chromosome-condensing factors, causing the sperm nucleus to undergo chromosome condensation prematurely. This anomaly appears to be related to incomplete nuclear and/or cytoplasmic maturation. Triploid zygotes (6.5% of fertilized oocytes) display an original type of division: half of them divide into 3 and 6 cells, whereas at the same time diploid zygotes divide into 2 and then 4 cells. A cytological study, using both antitubulin antibodies and Hoechst dye, allowed us to demonstrate that they divide into 3 cells by means of a tripolar spindle. Triploidy seems to be correlated with four of 16 clinical or biological parameters examined: semen origin (fresh or frozen), type of stimulation treatment, number of oocytes recovered and embryo morphology. Haploid eggs (1.6% of inseminated oocytes) result from parthenogenetic activation. A correlation was found between a high number of recovered oocytes and triploid zygotes, and the occurrence of oocyte activation. These data show that increasing follicular recruitment decreases the overall oocyte quality and maturity leading to an overall 9% with impaired fertilization.