No matter how important are new discoveries and methods, they cannot be considered to have reached fulfilment until generally applied to the sick. W. B. Castle, 1939* The development of a safe 7 and relatively simple method of doing percutaneous renal biopsies has provided the physician and the clinical investigator with a new and useful tool for the study of renal diseases.7,8 Elsewhere we have discussed in some detail its value to the patient and the physician.9 By its use, exact histologic diagnoses can be made which provide a sound background for etiology, diagnosis, treatment, and prognosis. The procedure has also been used to obtain cultures of organisms from infected kid- neys; to study, by serial biopsies, the natural history of diseases involving the kidney; to study reversible diseases of the organ, and to assess the effects of drugs on renal and cardiovascular diseases.10-21 Renal biopsies have