An acute phase response was previously found in cows at parturition, which might be associated with uterine cytokine release. Five late pregnant cows were implanted with vascular catheters in both the maternal aorta and uterine vein. Blood samples were taken to study temporal relationships between changing plasma levels of proinflammatory cytokines and the periparturient acute phase response following prostaglandin (PG)-induced luteolysis at Day 275 of gestation. The plasma levels of three proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and interleukin-6 (IL-6), as well as progesterone (P4), PGFM and serum amyloid A (SAA) were measured every 4 h between PG induction and expulsion of the calf. In the arterial plasma, progesterone levels dropped to baseline levels within 10 h following PG treatment, indicative of complete luteolysis. Contrary to expectations, the uterine vein samples showed lower proinflammatory cytokine levels compared with the maternal aorta values. A classical acute phase response, as assessed by SAA, was observed during the expulsive stage, but not during luteolysis.