Different floor space allowances for dry, pregnant sows in pens were evaluated to determine the impacts of space on sow behavior, immune, and cortisol measures. The experiment consisted of 6 replications (blocks 1 to 6; n = 20 sows/group), and within each replicate, physiological measurements were recorded for 2 consecutive pregnancies. A total of 152 sows were measured at 1 gestation, and 65 of those sows were measured at the successive gestation (n = 217). Groups of 5 sows/pen were assigned to 1.4, 2.3, or 3.3 m(2) of floor space/sow or of 5 sows in individual stalls (1.34 m(2)). Behavior measures were stand, sit, lie, walk, drink, oral-nasal-facial (ONF), sham chew, and aggression. Immune traits included both descriptive and functional aspects and cortisol. At d 90 ± 5 of gestation, the occurrence of ONF behaviors increased from 0300 to 1500 h, and lying behavior decreased from 0700 to 1100 h for sows kept at 2.3 m(2). Sows in stalls displayed more (P < 0.05) ONF from 1500 to 2300 h. Stand, sit, drink, ONF, and sham-chew behaviors were affected by floor space; sows in pens at 2.3 m(2) performed more ONF, and sows at 1.4 m(2) performed more sham chewing (P < 0.05). Standing (P = 0.05) and drinking (P = 0.06) were increased, but lying (P = 0.06) was reduced for sows in pens at 2.3 or 3.3 m(2). Sitting and drinking were greater but lying was less for sows in stalls compared with sows in pens (P < 0.01). Immune traits were affected by treatment (P < 0.05); neutrophils were less and lymphocytes were greater, resulting in a reduced neutrophil:lymphocyte (N:L) ratio (P < 0.05) for sows in pens at 3.3 m(2). Natural killer cell was greater but lymphocyte proliferation was less for sows in pens at 1.4 m(2) (P < 0.05). Sows in stalls had greater N:L ratio than sows in pens (P < 0.05). For sows in pens, linear and quadratic responses were detected for behavior and immune traits. As floor space increased, walking and aggression increased. As floor space decreased, neutrophils, N:L, and natural killer cell increased, but as floor space increased lymphocyte proliferation increased. On the basis of behavioral and physiological responses shown by sows in all 4 environments it is apparent that neither floor space nor stall environment provided adequate or quality of space to improve sow well-being. However, the differential behavioral and physiological mechanisms initiated by sows in response to their specific environment the sows were able to evoke the appropriate response(s) needed to adequately adapt to their environment.