About the time we submitted our second "A case for diagnosis" on a boy with acute renal failure [1], a 7-year-old girl was admitted to our renal unit with almost identical findings of acute renal failure with characteristics of both the haemolytic uremic syndrome (HUS) and acute glomerulonephritis. The child was born prematurely with a gestational age of 33 weeks. She stayed in the neonatology unit for 4 weeks. Her psychomotor development was mildly retarded and from the age of 3 years she had epilepsy which was first treated with sodium valproate and later carbamazepine. At the time of her acute renal failure she had been on carbamazepine only tbr about 1 year.After 5 days of loose stools, she was admitted to another hospital, mainly because of marked oedema. She was pale, had facial and pretibial oedema and a blood pressure of 110/70 mmHg (95th percentile). Her serum creatinine was 3 mg/dl and urea 360 mg/dl. She was oliguric and urine microscopy showed too numerous to count red blood cells (RBC) and 3+ proteinuria. The peripheral blood count showed a haemoglobin of 11.2 g/dl, 12,800 white blood cells (WBC) and 222,000 platelets/gl. She was prescribed bed rest, sodium restriction and frusemide. Over the next 5 days her haemoglobin dropped to 8.2 g/dl and platelets to 95,000/gl; urine output and serum creatinine improved, but her blood pressure rose to 164/96 mmHg. She was referred to us for diagnostic investigation.We saw an ill-looking, pale girl with eyelid oedema, no skin lesions, normal tonsils and a blood pressure of 160/ 120 mmHg. She had macroscopic haematuria with a urine output of 558 ml/24 h which contained 440 mg of protein.Her haemoglobin was 10 g/dl, WBC count 14,800 and platelets 192,000/pA. Serum haptoglobin was 0.14 g/1 (normal value 1-3 g/l). Serum electrolytes were unremarkable, creatinine was 1.7 mg/dl and urea 96 mg/dl. Creatinine clearance was 36 ml/min per 1.73 m 2. Plasma renin activity was 1.09 ng/ml per hour (normal value fo age 1-5). Serum protein electrophoresis showed a lowish albumin of 3.5 g/dl but elevated gammaglobulins of 1.66 g/ dl. Total complement was less than 100 U/ml (normal value 300-500 U/ml) with normal values for Clq, C3 and C4. The antistreptolysin (ASLO) titre was 1,180 IU/ml (normal value <200). Throat culture was negative for beta-haemolytic streptococci. Renal ultrasound showed two normalsized kidneys with a hyperechogenic cortex. With acombination of atenolol, nifedipine and enalapril, her blood pressure normalised progressively.A renal biopsy was performed. Light microscopy showed eight glomeruli with diffuse mesangial proliferation with a circumferential crescent in two. Tubuli and vessels were unremarkable, the interstitium was somewhat oedematous. On immunofluorescence (10 glomeruli), only C3 could be identified in a subendothelial position.At discharge 2 weeks later her blood pressure was 96/ 50 mmHg and serum creatinine 1.1 mg/dl. The urine had 1,500 RBC/gl by direct counting and proteinuria was only 40 mg/24 h. She was investigated again 6 months later, wh...