The influence of transport stress on the secretion of adrenocorticotropin (ACTH) from peripheral bovine lymphocytes was evaluated by exposing cows to short- (30 min) or long-term (14 h) transport. After transporting animals for 14 h they were given a mandatory rest for 24 h in two different situations, either by off-loading them and allowing them to rest in a stall or by keeping them in the truck. Blood samples were withdrawn before and after transport and after the rest period in long-term transported cows and before and after transport in cows transported for 30 min. Peripheral blood lymphocytes were separated and cultured for 72 h in serum-free medium. Adrenocorticotropin was measured using highly sensitive and specific immunoradiometric assay in culture supernates. We noticed no effect of short-term transport on ACTH secretion from lymphocytes. The ACTH concentration in animals transported for 14 h increased (P < or = 0.01) from 4.72 +/- 0.48 pg x mL(-1)/2 x 10(6) lymphocytes before the transport to 8.24 +/- 1.40 pg x mL(-1) directly after the transport. When animals were off-loaded and rested in a stall for 24 h, ACTH secretion from cultured lymphocytes returned to the basal value of 4.24 +/- 0.31 pg x mL(-1), whereas the animals rested in the truck had ACTH levels of 8.9 +/- 1.43 pg x mL(-1). Phytohemagglutinin, a plant lectin that stimulates lymphocytes, did not affect the lymphocytic ACTH secretion in this study. Heart rate and rectal temperature measured telemetrically increased in cows directly after 14 h of transport but decreased to pretransport values in cows rested for 24 h in cows rested in stalls and those rested inside the truck. This experiment is the first to show lymphocytic ACTH secretion in cows, and the results indicate that ACTH secretion from peripheral lymphocytes could be used as a reliable measurement in stress studies.