Sow housing is one of the most controversial welfare issues facing the swine industry. New housing systems are being implemented without scientifically evaluating the impact these alternative systems have on well-being. The objectives of this study were to evaluate a) the effects of 3 housing systems on sow physiology (Exp. 1) and more specifically b) the utilization of individual vs. group space in the free access stall treatment (Exp. 2). On d 30 of gestation 12 multi-parious sows were allocated to a standard crate (CRATE; control), an adjustable crate (FLEX), or free access stall-pen (FREE). On d 89 of gestation, FLEX width was adjusted to achieve 2cm space between sow and stall. Immune and endocrine status was measured on d 0, 30, 31, 89, 90 (FLEX only) and 110. For Exp. 2 live behavioral observations among sows in FREE system were registered for 60 min on d 30, 45, 60, 75, 89, and 103. Data were analyzed using Proc MIXED with repeated measures (SAS). In Exp. 1, on d110, phagocytosis was greater (P<0.05) among sows in FREE than sows in FLEX. Sows in FREE and FLEX stalls had less concanavalin A- (P<0.001) and lipopolysaccharide- (P<0.05) induced proliferative responses at d31 and throughout gestation. Sows in FREE had greater (P<0.05) cortisol on d89 than previous days of gestation. In Exp. 2, regardless of day of gestation, some sows spent a greater (P<0.05) amount of time in group-pen area than in individual stall. Later in gestation, fewer sows spent more time in the group-pen than on d30 (P<0.05). These data indicate that housing systems can affect immune function and physiology of the sow throughout gestation; while FREE can affect individual sow preference on space utilization. Thus it is important to assess the impact of housing components on sow-well being.