<p>The purpose of this study was to investigate the presence and incidence of specific protein bands on the Nelore bulls' seminal plasma, fit for reproductive activity complete or partially. There were used 68 samples; 20 of the Census and 48 of the Blunt variety, with an average age of 4 years. In the scrotum perimeter (35,05 ± 0,49 cm and 33,30 ± 0,39cm), corporal mass index (302,62 ± 5,87 and 284,19 ± 5,15 Kg|m2) there was difference (p &lt; 0,05) between the Census and Blunt varieties respectively. With regard to corporal weight (627,70 ± 11,37 and 611,58 ± 8,66 kg); height (1,44 ± 0,01e 1,47 ± 0,01m); ejaculation volume (5,82 ± 0,48 and 5,17 ± 0,29 mL), progressive spermatic motility (73,50 ± 2,81% and 75,62 ± 0,97%), spermatic vigor (4,30 ± 0,19 and 4,27 ± 0,11) and mass motility (4,27 ± 0,11 and 3,33 ± 0,23) there was no difference (p&gt;0,05). In spermatic morphology, neither was there inequality between Census and Blunt varieties, with 5,06 ± 8,20% and 5,32 ± 6,40% of mayor defects respectively; 9,91 ± 6,74% and 8,36 ± 6,06% for the minor defects; and 14,76 ± 13,20% and 13,82 ± 12,61% for total defects. The electrophoresis of the seminal plasma revealed protein bands with weights between 5 and 105KDa. In 100% of bulls fit for reproduction, there was found protein with a weight of 13Kda, as well as bands of 20KDa. The other protein bands showed their presence with different incidence percentages in bulls totally or partially fit for reproductive activity. Both of the studied varieties made evident the effective reproductive adaptation under similar climate conditions.</p>