Sulfamerazine (monomethylsulfadiazine) was synthesized by Roblin and his co-workers1 and has been used by several investigators in the treatment of a variety of clinical infections.2 Since its therapeutic activity is apparently comparable to that of sulfadiazine, sulfathiazole and sulfapyridine, it is important to determine whether it possesses any advantage over those drugs with regard to toxic reactions. Evidence is conclusive3 that sulfadiazine is less toxic than sulfathiazole and sulfapyridine, and for this reason it is recommended more frequently for systemic use than any other sulfonamide at the present time. In order to evaluate the toxicity of the more recently introduced sulfamerazine, we have at this time reviewed the records on all the patients observed by us to whom sulfamerazine4 or sulfadiazine4 was administered. These patients were in the wards of the Gallinger Municipal Hospital5 or in the private practice of one of us. Altogether