I IOpa IC WI sys emlc Iseases Renal vein thrombosis Obstruction U ric acid crystals Stones Tumours-benign and malignant Fibrosis Strictures 2 Acute and Chronic Renal Failure (ARF) depends on biochemical tests, which are fortunately simple to perform and are commonly available. However, the clinician has to think of the possibility in order to test the diagnosis. Frequently, patients are admitted to a renal unit from medical, surgical or gynaecological wards where the development of ARF has gone unrecognized, either because the relevant investigation has not been performed or because the result has been overlooked. This happens because ARF occurs in patients with complex problems which themselves demand con­ siderable attention, and it is easy to overlook a comparatively rare, if important, complication.