Greyhounds are usually transported by air between Ireland and England in wooden kennels similar in size to greyhound racing starting traps. These kennels have been criticised in the belief that their small size leads to unnecessary stress. The present study compared plasma ACTH, cortisol, lactate and non-esterified fatty acid concentrations in 12 greyhounds transported either in the existing wooden kennels or in wider perspex kennels, which were stowed either in the belly hold or in the main cargo hold of jet freighter aircraft. Increased kennel size did not appear to result in decreased stress responses but there was a significantly greater stress response in the dogs kept in the belly hold of the aircraft. Individual variation between dogs was the most significant feature of the study.