The catalytic activity of phospholipase A 2 (PLA 2 ) was measured in serum samples from 32 crocodiles in Thailand and Australia by a method using 14 C-oleic acid-labelled autoclaved Escherichia coli membranes as a substrate. The highest PLA 2 activity was measured in the serum of Crocodylus siamensis (n = 9, mean ± SD), 13.3 ± 3.1 U/l followed by hybrid C. siamensis × C. porosus (n = 6), 10.4 ± 8.7 U/l and Crocodylus porosus (n = 17), 4.3 ± 3.0 U/l. The difference between C. siamensis and C. porosus was highly significant (P < 0.001). The gender of the animals and the geographical location of the crocodile farms were not significant variables affecting serum PLA 2 levels. It was concluded that PLA 2 is present in crocodilian serum and may have an antimicrobial role.