We currently recommend using the synthetic ACTH product cosyntropin (Cortrosyn®; Organon Pharmaceutical) for ACTH response testing in dogs and cats. To reduce reagent cost, consider using the mini-dose regime: measure serum cortisol before and 1 hour after IV administration of 5 µgm/kg cosyntropin. The reconstituted vial can be stored refrigerated for up to 2 months without loss of bioactivity.