Feral cat and stoat control is conducted in New Zealand to protect a number of threatened native species, including kiwi, from predation. Para-aminopropiophenone (PAPP) is being developed for predator control. Previously reported cage trials have shown PAPP presented in a meat bait was palatable and effective, while symptoms observed demonstrated PAPP to be humane. Subsequent field trials on stoats were undertaken in two blocks of native forest and achieved 83% and 87% reductions in the stoat abundance index, and a field trial on a population of radio-collared feral cats had an 84% kill. PAPP represents one compound from a new class of active ingredients, which we are calling red blood cell toxins. These vertebrate pesticides have humaneness, and low secondary and non-target poisoning risks, as their primary consideration. The dose is optimised to be effective in the field and reduces oxygen supply to the brain such that animals become lethargic, sleepy and unconscious prior to death within 1-2 hours. Results from these field trials on stoats and feral cats indicate that PAPP will be a useful additional tool for predator control.