The present study was carried out to investigate the relationship between sperm subpopulation kinetics on in vitro fertilization rate. The ability of human sperm to achieve fertilization oocytes was investigated in relation to particular motility parameters obtained on a computer aided sperm analysis system base. Analysis covers velocity straight linear (VSL), cross beat frequency (CBF), lateral head displacement (LHD) and homogeneity of progressive motility velocity (HPMV) of fresh semen and semen after density gradient selection. Investigation was based on sperm samples from 82 infertile couples undergoing IVF. Two subpopulations were extracted from each sample using the clustering method with respect to VSL parameter: a slow and rapid one. Comparison of obtained results before and after selection shows no significant change of subpopulations percentage. However, this method of selection strongly influences motility parameters of both subpopulations. There was found a positive correlation for VSL, LHD and HPMV and a negative correlation for CBF parameters found in slow fraction of fresh semen and percentage of fertilized oocytes. On the other hand, rapid subpopulation parameters for fresh semen and parameters found for both subpopulations in semen after selection did not correlate with one. This means that information of slow sperm subpopulation kinetics carries important prognostic value of IVF success. Since the current prognosis factors ignore motility parameters of slow sperms, our results show the importance of such an analysis.