Carbon dioxide production by fasting immature Estuarine crocodiles was between 0·023 and 0·042 mlg-1h-1. The calculated oxygen consumption was between 46% and 70% of that expected from the crocodiles weights. The daily percentage weight loss while fasting is given by 0·020 + 0·584 (days without food)-1. Survival time of crocodiles that failed to feed after hatching was related to initial weight, death occurring after 27·4% of the initial weight had been lost. Fat was the principal nutrient catabolized by fasting crocodiles. The results are consistent with those expected of an inactive predator that rapidly lowers metabolic rate to starvation levels when food is unavailable and can thus withstand extended fasts.