The use of boars rather than barrows for pork production could carry significant financial and animal welfare incentives, since boars grow much more efficiently than barrows, and the routine castration of young piglets could be avoided. Aside from the issue of boar taint, the potential for increased aggressive and sexual behaviour among groups of boars requires further investigation. A comparison of aggressive and sexual behaviour between groups of boars and barrows was conducted. Overall, boars were consistently more active in both aggressive and sexual behaviour throughout the final 12 weeks of the production cycle (weeks 10-22). Correlations between plasma androgen levels and behaviour were investigated, but the results were inconclusive. A second experiment tested the effect of topically-applied androstenone on post-mixing aggression in market-weight boars and barrows. A tendency for treated pigs to spend less time fighting during the initial 2 hours post-mixing was detected, although problems with the experimental design prevented our formulation of firm conclusions regarding the treatment's efficacy.