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The effect of group housing sows during early pregnancy on maternal endocrine changes and on embryonic survival was studied. Twenty crossbred (Swedish Yorkshire× Swedish Landrace) primiparous sows were used. On day 11±1 of pregnancy 3 unacquainted sows were randomly assigned to a single pen measuring 3m× 3m in area. A fourth sow in each group was housed in an individual pen and used as a control. This procedure was repeated 5 times to collect data from 5 animals in each rank as well as in a control group. Blood samples were collected from the day before grouping to day 5 after grouping for Cortisol, corticosteroid-binding globulin (CBG), progesterone (P 4), oestradiol-17β (E 2) and prostaglandin F 2α metabolite (PG-metabolite) analysis. A rank-order test and an ACTH test were performed on day 4 and day 5 of grouping respectively. The sows were slaughtered on day 17±1 of pregnancy …