The behaviour of 31 to 43 pregnant sows housed in one pen was observed during 5 diurnal periods (the number of sows depending on the timing of parturition). On the basis of these behavioural observations the sows were distributed into 5 social ranks: dominants, subdominants, subordinated, self-possessed and marginals. The reproductive traits studied were: number of live-born piglets, number of piglets alive at 21 days, and litter weight at 21 days. Reproductive performance evaluated in this way did not show any distinct differences according to the social ranks of sows. The average number of piglets born alive varied from 10.8 in self-possessed to 12.7 in the two extreme ranks: dominants and marginals. The number of piglets alive at 21 days varied from 10.5 in self-possessed to 12.3 in marginals. Litter weight at 21 days varied from 58.0 kg in subdominants to 59.7 kg in marginals. It is suggested that the electronic feeding system is advantageous for the housing of pregnant sows. This feeding system enables maintenance of pregnant sows in one group and permits undisturbed and individual feed consumption irrespective of sows social rank.