Abstract: In mice the acute oral toxicity cf primaquine gulonate was lower than that of primaquine phosphate, but the antimalarial activity (ED_50) was similar to the latter, in rats, rabbits and dogs, the subacute toxicity was also found to be low. In clinical trials, the preveution of relapse of vivax malaria, both of them showed the same efficacy, the main side effect such as cyanosis, primaquine gulonate was less marked than those administered with primaquine phosphate.