In your discussion on the campaign against animal research (Nature 483, 373–374; 2012), you mention a study in macaques that has moved into early clinical trials in humans, with promising results. Sadly, there is a yawning chasm between early promise in trials and efficacy.

The US Food and Drug Administration reports that more than 90% of trials fail (see go.nature.com/h2365q), even though the treatments tested, by definition, were considered sufficiently efficacious and safe in animals to merit a clinical-trial licence.

Many other treatments to protect the brain after stroke have failed in humans, despite success in rodent and primate trials (V. E. Collins et al. Ann. Neurol. 59, 467–477; 2006). None of the 85 or so candidate HIV vaccines that were effective in primates has so far worked in humans (J. Bailey Altern. Lab. Anim. 36, 381–428; 2008). The monoclonal antibody that caused severe inflammatory reactions in a 2006 clinical trial at Northwick Park Hospital, London, caused no problems in primates at 500 times the dose given to the human volunteers.

The public is rightly concerned about the transportation of primates for questionable experimental purposes. These cannot justify the degree of suffering involved during capture, in breeding and holding facilities and during lengthy transportation (see go.nature.com/svbuvj).