Gantrisin,® previously designated NU-445, is 3,4-dimethyl-5-sulfanilamide isoxazole. Since early in 1946 this sulfonamide has had rather extensive experimental and clinical trial,1and all observers repeatedly emphasized the apparent low toxicity of the drug. Though infrequent, the usual toxic phenomena incident to the use of other sulfonamide compounds have been noted, including dermatitis,2anorexia,3nausea, vomiting,4headache,5fever,2a, hvertigo,2f, gcrystalluria6and hematuria.7A review of all available published clinical reports to date discloses only eight instances of leukopenia.2f, gNeutropenia of moderate degree was present in two of these eight cases. In neither of the two cases were neutrophils depressed below 30 per cent.8However, in several clinical reports specific mention of leukocyte counts was not made. The present case of true agranulocytosis due to gantrisin® is reported because: (1) to our knowledge this is the first instance