Aim. To assess the morphological and functional characteristics of spermatozoa and DNA stability in patients with normal seed parameters and with an ITZ exceeding the threshold value.
Patients and methods. 85 males were studied for semen quality parameters. The morphological anomalies of head, middle piece, and tail of spermatozoa were estimated and presented in illustrations. Due to results elaborated the index of teratozoospermia was calculated. Then the Comet assay was performed.
Results. It has been found that spermatozoa from patients with high teratozoospermia index possessed decreased motility as compared to ones from patients with low index of teratozoospermia. It was not found any difference in concentration of spermatozoa between groups of males which possess low and high index of teratozoospermia. The spontaneous frequency of DNA damage estimated by means of single cell gel electrophoresis followed by silver staining in spermatozoa from healthy donors did not exceed 3,1±0,6. The frequency of DNA damages in sperm of patients with abnormal index of teratozoospermia exceeded 39,6±7,4% (p<0,01).
Conclusions. Our results suggest that minor morphological changes in spermatozoa do not affect their motility, while significant morphological abnormalities with ITZ exceeding threshold values are closely associated with impaired DNA stability and dramatically reduce the quality of patient’s seed.
Summary. In the initial assessment of patient fertility the attention should be focused on a comprehensive study of sperm DNA morphology and stability.

Keywords: morphology of spermatozoa, teratozoospermia index, comet assay