The relationships between 41 genetic markers (blood groups and biochemical polymorphisms), 3 environmental factors (season, management before the Lidia ("encierro"), punishment suffered), body constitution, and pedigree on the one hand, and the activity of muscular enzymes in serum, creatine kinase (CK), lactate dehydrogenase (LDH), aspartate transaminase (AST)) on the other, were analyzed in 179 fighting bulls. The C system of cattle blood groups and the "encierro" were significantly related to the activity of the muscular enzymes of the studied animals. The fighting bulls with the W1 and C1 antigens had a higher CK and LDH activity respectively, whereas the fighting bulls with the X1 antigen as well as those that participate in the "encierro" had a lower AST activity. This results could suggest a lesser degree of muscular injury during the Lidia in animals with X1 antigen, in those that participate in the "encierro", and in those without W1 and C1 antigens.