Criollos is the oldest cattle breed in America and the world at large. The origin dates back to the first cattle brought by C. Columbus. They are well known for their toughness and longevity. Their genetic variability is another advantage to be taken into account in crossbreeding because it ensures high hybrid vigor. The objectives of the present study were to determine computer-assisted sperm analysis (CASA) motility parameters and sperm morphology of Criollos bull semen (brought from Parque Nacional Los Glaciares, Patagonia, Argentina) v. other Bos taurus semen. A total of 29 ejaculates of different adult bulls (Angus and Hereford) and 25 ejaculates of Criollos bulls were evaluated in an artificial insemination center between December 2004 and December 2005. Semen collection was done by electroejaculation (EE) in all breeds. Fresh semen was diluted in a semi-defined semen extender (Andromed; Minitüb, Tiefenbach, Germany) and frozen in an automatic freezer (Digicool, IMV, Paillette Crista, France). Stain morphology was done using eosin/nigrosin, and evaluated in an optic microscope with phase contrast. Parameters of volume, total concentration (CONC), motility %, motile progressive sperm %, velocity average path (VAP, μm s^–1), velocity straight line (VSL, μm s^–1), curvilinear velocity (VCL, μm s^–1), and linearity (LIN, %) were determined by CASA (HTM-ceros 12.1, Berkley, CA, USA). The results obtained were analyzed statistically with a one-way ANOVA test and are summarized in Table 1. Results from the sperm motility analysis indicate that there were no significant differences (P > 0.05) in CONC, motility %, motile progressive %, or VSL between Criollos and other B. taurus bull semen. VAP and VCL rates were significantly higher in Criollos bull semen than in other B. taurus semen, and LIN was lower. Also, there was a significant difference in volume collected between both breeds. Regarding sperm morphology, Criollos bull semen is at the maximum limit acceptable for head defects (detached heads: 15%). These results suggest that Criollos bull semen is not different from other Bos taurus semen; however, it does show different velocity and linearity rates.