For the past five years one of us (Dr. Schick) has been studying the disease that follows the administration of nirvanol (phenyl-ethylhydantoin), the drug used so widely in the treatment of chorea. The name "nirvanol sickness" was originated by von Pfaundler, who compared the disease with serum disease. There exist in both diseases a time of incubation of similar duration, a fever, rash, edema, leukopenia with relative lymphocytosis, eosinophilia, swelling of the lymph glands and other symptoms. Other similarities were pointed out by Payne and de Rudder, such as an alkalosis during the time of incubation, which changes to acidosis at the outbreak of the rash. According to the literature well developed nirvanol sickness improves the symptoms of chorea. Children show nirvanol sickness more frequently than do adults. Barbital and phenobarbital are also able to produce symptoms similar to those produced by nirvanol, although less frequently. Apparently, all of these