Inbreeding reduces quality and survival of offspring due to increased homozygosity and the expression of recessive deleterious mutations. However, there are only few studies examining how inbreeding affects behavior in adults. We aimed to replicate an earlier study in wild house mice by inducing a stress factor - infection with Salmonella. To examine whether less inbred males are more aggressive and have a higher probability to win brief encounters, we confronted full-sib inbred and outbred males in a neutral arena and recorded aggressive as well as defensive behaviors. Contrary to our expectations, any effects of inbreeding on aggressive and defensive behaviors were not dependent on infection status. Furthermore neither infection treatment nor inbreeding affected the amount of aggressive and defensive behaviors displayed by males. Short-term aggression assays may be a useful tool for investigating certain aspects of aggressive behavior; however, long-term aggression assays might be more suitable to monitor all aspects of competitive ability and antagonistic interactions as well as effects of certain treatments on competitive ability and aggressiveness. These results may have important implications for opposed selection pressures arising from female choice and male-male competition.