A diabetic woman presented with diabetic ketoacidosis after demonstrating immediate-type hypersensitivity to heterologous insulin. She had had interrupted insulin therapy in the past. Insulin requirements during the course of treatment for the acidosis suggested marked resistance, with 50,000 U of insulin needed in the first 36 h. Anaphylaxis requiring intubation and emergency treatment developed after intravenous purified pork insulin was administered. Elevated titers of insulin-specific IgG (441.6 U/L serum) demonstrated immunologic insulin resistance. Positive intradermal skin tests for beef and pork insulins and detection of insulin-specific IgE by RAST assay revealed concurrent immediate-type allergy. A review of the literature revealed the unique occurrence in this patient of simultaneous ketoacidosis, insulin allergy, anaphylaxis, and immunologic resistance. Interrupted insulin therapy in susceptible individuals remains a potential danger, even with the availability of purified insulin preparations.