A 3½ year old Negro boy with an obscure syndrome of inexplicable, transient, acquired hypoproteinemia, involving plasma albumin and especially gamma globulin, has been observed. Edema, oliguria and weight gain were noted 10 days following an attack of acute tonsillitis. Hypertension, renal impairment, proteinuria and hematuria were conspicuously absent, and an associated eosinophilia subsided as recovery progressed. Plasma protein regeneration was complete in 10 weeks. The patient has since developed mild asthma but has otherwise remained well. This appears to be an unusual case of transient derangement of plasma protein metabolism. Possible relationships to the syndromes of acute nephritis without proteinuria, nephrosis, serum sickness and idiopathic acquired hypoproteinemia are discussed.