In most cases the control of dermatitis herpetiformis may be readily achieved with sulfamethoxypyridazine. It is impossible to predict the level of maintenance dose necessary to suppress the clinical reaction, and it is similarly impossible to predict the blood levels achieved with any single unit dosage. Adverse reactions deter from the over-all usefulness of the drug. The adverse reactions observed concerned principally the skin and hematopoietic system. In addition, the gastrointestinal and central nervous system showed evidence of toxicity. The dermatological manifestations followed almost all known previously reported reactions to sulfonamide drugs. The administration of this drug requires routine assay of the blood for sulfamethoxypryidazine levels. It is the duty of the clinician to balance the benefits to be derived from any drug against the risks of its administration.