Fertilization is the process of paternal and maternal chromosomes uniting in the activated oocyte. The most frequent reason for fertilization failure is sperm incapacity to penetrate into the oocyte. In such cases the gametes can be united mechanically, but the fusion of their chromosomes is resigned to the action of the ooplasm. The condition required for uniting is synchroneous decondensation of paternal and maternal chromatin and formation of a male and female pronucleus. Chromatin transformation is not always coordinated, which may lead to fertilization arrest. With the technique of immunofluorescent microscopy of oocytes failing to fertilize, allowing the simultaneous observation of chromatin and pertaining microtubules – the most important structures for chromosome dynamics during fertilization, we can establish anomalies in the process of gamete union and elucidate some of their causes.