BACKGROUND: A 55-year-old woman with vitiligo, hypothyroidism, interstitial lung disease and diabetes mellitus developed severe insulin resistance during a hospital admission for respiratory failure. Before hospitalization, her HbA(1c) level was 8.1% on approximately 100 U/day of insulin. Her interstitial lung disease had been treated with glucocorticoids, but after their withdrawal her insulin requirements had increased dramatically. She remained hyperglycemic (blood glucose levels 16.7-27.8 mmol/l), despite intravenous insulin at doses as high as 30,000 U/day. INVESTIGATIONS: The patient's serum creatinine level was 301 micromol/l and her liver function tests were normal. A mildly elevated white cell count was present. The patient was diagnosed with pneumonia due to Pseudomonas aeruginosa. When the patient's plasma glucose level was 22.5 mmol/l, her plasma C-peptide level was 0.9 nmol/l and her serum insulin level was 294 pmol/l. At that time the patient was on 2,600 U/day of intravenous insulin aspart. Anti-insulin and anti-islet-cell antibodies were not detected, but anti-insulin-receptor antibodies were found. DIAGNOSIS: Type B insulin resistance syndrome. MANAGEMENT: The patient's insulin resistance responded to glucocorticoids and plasmapheresis. After the patient was treated with prednisone (60 mg/day), her insulin requirements decreased within 1 week to pre-admission doses. When steroids were subsequently discontinued, glycemic control deteriorated once again. Plasmapheresis was initiated, inducing a striking acute decline in insulin needs. On a maintenance dose of 10 mg prednisone/day, glucose control improved (HbA(1c) 5.8%) with an average of 60 U of isophane insulin twice daily.