The present review describes the behavioral characteristics of bulls raised under tropical and subtropical conditions and emphasizes the difficulties associated with adequately monitoring their performance in the field to predict reproductive potential. Most of the information generated for improving our understanding of bull behavior under range conditions has been generated in Bos taurus bulls. The limited information available in Bos indicus indicates that males searching for cows in estrus display different sexual patterns when compared to B. taurus bulls and a poor selection of a sire utilized in range conditions can have an important impact in cattle production. Screening and selecting [cg1] bulls for desirable reproductive traits and high libido is known to improve the reproductive performance of the herd. The reproductive and genetic potential of a bull is influenced by factors such as management, age, nutrition and problems related to the female such as embryonic death and anestrus. However, behavioral characteristics of bulls when detecting and serving cows in estrus is poorly understood.