Fifty-four beef bulls with an average age of 21 months and representing nine breeds were evaluated for libido using two types of tests. The serving capacity (SC) test was repeated five times on groups of bulls and was followed by an individual test. In the SC test, breed significantly influenced the number of services completed in 30 min. Bulls showed a highly significant improvement in their SC as their experience increased but this did not apply to all breeds. There was thus a significant breed by test interaction. Agonistic interactions had no influence on SC although exceptions were noted. Age, mass, physical size, scrotal circumference, semen quality, and environmental temperature (10,5- 26,5 °C) did not influence SC. There was a highly significant correlation (r = 0,664) between SC and the number of services completed on the individual test. Of the bulls tested, 27,7%, 40,4%, and 31,9% were classified as having a low, medium, and high libido.