I N 1939, Poul Iversen and Kaj Roholm, in Copenhagen, published their report on aspiration biopsy of the liver. Kaj Roholm had developed a special cutting needle with attached syringe to do this (Fig 1). Soon after the end of World War II, Iversen and Brun began to use Roholm's needle on kidneys (P. Iversen, personal communication). In 1946, I returned to Boston to work once again on the liver, blood, and food. After 6 years in military service, I had to reorient myself to civilian medicine at the Mayo Clinic. I worked for 3 months on Snell's liver service. I hurried back to Boston with Vim-Silverman needles, which Snell's team used on patients' livers. Like others, I aimed at a patient's liver and pulled out kidney tissue. No harm resulted. It was obvious one could deliberately biopsy the kidney to diagnose Bright's disease. This idea excited me. Elsewhere2 there is described how the late Hans Popper arranged for me to visit Poul Iversen and Claus Brun in Copenhagen, who were doing aspiration biopsies of the kidneys; I had serious reservations with its use: the patients were upset and there was a low yield of tissue. In Chicago, I enlisted Robert C. Muehrcke, a medical student, and Murray Franklin to develop the FranklinVim-Silverman needle (Fig 2). Reference 2 described how we developed the technique of percutaneous renal biopsy (PRB) in the prone position. It was an exciting time. In those early years between 1950 and 1960, every renal biopsy taught us something new and remarkable. In 1936, Jean Hamburger, renowned physician and writer, received his PhD from the Sorbonne (Physiology de ['innervation renal, Paris, Mason et cie). In 1959, he was appointed Professor of Medicine at the University of Paris and organized a renal unit in the Hospital Neckar. This was to play an important role in the development of PRB. Hamburger and his colleagues had produced an effective biopsy needle, which was the forerunner of early commercial ones. In addition, his unit became a major center for nephrology, and for the study of immunology in the diagnosis and treatment of renal disorders, especially transplantation. In Boston, a major center for nephrology, John Merrill, David Hume, George Thorn, Gustave Dammin, and their colleagues began to use renal biopsies to study homotransplantation in 1954. Later, biopsies were done on a wide variety of renal disorders. These were performed by the st!,lff, including Donald Oken and many others. In 1951, Conrad Pirani started to grade the various structures seen on biopsy sections from 0 to 4 +. Clinical pathologic correlations were attempted. From his histologic evaluations, one obtained the maximum useful information from renal tissues. This made an enormous difference to the total care of patients. In 1954, Muehrcke et al suggested the use of serial renal biopsies. 3 This illuminated studies on the natural history of diseases and disorders of the kidney, and we began to recognize the effects of treatment, with agents such as corticotropin. Between 1954 and 1957, we published observations on lupus nephritis and other collagen vascular disorders.4 It was apparent that one could make new approaches to pathologic analysis of the dynamic state of a disease and decide if there were florid, moderate, or minimal changes present. Pirani introduced the ideas of local, focal, and diffuse changes, with or without nephron dropout or base-