Semen was collected from Polish Halfbred stallions. Twenty individuals from 3 to 4 years of age were selected for the study. At least one ejaculate from each stallion was collected and assessed. Sperm morphology was evaluated using Papanicolaou stain, SpermBlue®, and a complex of eosin and gentian stain, whereas unstained slides were used as control samples. Morphometric measurements were performed on 100 randomly selected sperm heads in each ejaculate. The length, width, perimeter, and surface area of the sperm head were measured. The frequency of nuclear vacuoles was determined as well. Tygerberg’s strict criteria, which most precisely characterise the sperm head, were used in the morphological evaluation of the sperm. The results obtained indicate that in the case of staining with SpermBlue® and with eosin+gentian complex, the morphometry of the sperm head seems to be most similar to that observed in unstained smears. It also seems that neither shrinking nor swelling is uniform in the various staining techniques (Papanicolaou stain). Moreover, it appears that in comparison with unstained sperm, all methods caused the width of the head to increase as a result of swelling.