The medicinal leech, Hirudo medicinalis, has been recognized by plastic surgeons for its ability to reduce congestion and improve blood flow in grafted skin flaps by withdrawing excess blood. The leech's ability to digest blood is due to the presence of Aeromonas hydrophila in the gut of the leech. In this report we describe the occurrence of Aeromonas hydrophila septicaemia in rabbits used in a study to evaluate the efficacy of the medicinal leech on abdominal skin flap survival. In New Zealand White rabbits, twin 5 x 10 cm abdominal skin flaps were prepared and the epigastric vein was ligated to produce a model of venous congested skin. After 12 hours, a leech was applied to one of the congested abdominal flaps and skin survivability was assessed and compared with the unleeched flap. Five rabbits died acutely approximately 24 hours post-operatively. Gross necropsy, bacteriology and histopathology findings indicated that A. hydrophila was the causative agent of the septicaemia-toxaemia syndrome with an associated pneumonia and typhlitis. Review of the management and the experimental surgery protocol suggested that the two major disposing factors of Aeromonas septicaemia in these rabbits were stress and excessive prophylactic administration of penicillin.