This study examined the effects of environmental enrichment on aggressive behaviour and dominance relationships in growing pigs. Three hundred and twenty pigs were reared from birth to 15 weeks of age in either barren or enriched environments. The barren environments were defined by common intensive housing conditions (ie with slatted floors and in terms of recommended space allowances), while the enriched environments incorporated extra space and substrates for manipulation. Aggressive behaviour was observed in a social confrontation test during the suckling period and dominance relationships were assessed from a food competition test at 12 weeks of age. Animals were weighed at regular intervals throughout the experiment. Environmental enrichment reduced the expression of aggressive behaviour. Pigs from enriched rearing environments fought significantly less with unfamiliar animals than those from barren environments when tested under standard conditions (mean of 1.46 vs 2.75 fights per 30min test for enriched vs barren environments; SEM 0.20, P < 0.001). The nature of dominance relationships also appeared to differ between barren and enriched environments. In barren environments, dominance among pen mates was correlated with aggression (r = 0.33, P < 0.01), whereas in enriched environments it was correlated with body weight (r = 0.24, P < 0.01). Correlations between behaviour in the social confrontation and food competition tests suggested that dominance characteristics were established early in life and remained stable through the growing period.