Relationships between maternal liver and fetal brain and liver ornithine decarboxylase (ODC) activity and porcine fetal development were investigated. Yorkshire gilts were subjected to prolonged inanition (40 days; 0 kcal/day; water only) from day 50 to day 90 of gestation and, on day 90, hysterectomized or realimentated to a full diet and allowed to advance to term; controls received a full diet (7028 kcal/day) until hysterectomy at day 90 or throughout pregnancy. ODC activity was determined in maternal liver tissue collected from 6 experimental and 6 control gilts on days 50, 70, 89 and 91. ODC activity of day 90 fetal brain and liver tissue was also determined in 6 fetuses from each of 3 additional experimental and control dams (36 fetuses). Prolonged inanition of gilts during late pregnancy had a marked effect upon maternal liver ODC activity. Liver ODC activity in full-fed gilts remained constant across days, with a mean activity of 59 (pmol CO2 released/60 min per mg soluble protein). ODC activity before inanition (day 50) in experimental gilts was similar to that of controls but day 70 and continuing to day 89 (during inanition) was reduced > 7-fold. After 1 day realimentation (day 91), ODC activity had increased by > 10-fold, to levels similar to controls. Day-90 fetal brain ODC activity in inanition gilts was greater than the activity observed in control gilts, and fetal brain weights were similar in all dams, suggesting that ODC may play a role in maintenance of normal fetal brain development. ODC activity of day-90 fetal liver tissue was decreased in inanition as compared to control gilts, as were fetal liver weights. Reproductive performance, as determined by fetal survival rates, body weight, litter weight and size, was similar in inanition and control gilts. Changes in ODC activity may play a role in compensatory responses of the porcine dam and fetus during periods of severe nutrient deprivation to allow normal fetal survival and development.