AbstractOver 1,000 needle biopsies have been carried out at University College Hospital in London. Needle biopsy has been used by us for histochemical and electron microscopic examination of muscle during the diagnosis and treatment of neuropathic and myopathic disorders, for the diagnosis of mitochondrial myopathies, to study the course of recovery in polymyositis, and for investigations into muscle changes in systemic lupus erythematosus (SLE) and other autoimmune conditions. We have developed a microprocessor system for the measurement of muscle fiber areas, and needle biopsy specimens provide suitable material for such measurements. We have also used needle biopsy specimens for studies of protein turnover using stable isotopes and for trace metal and electrolyte analyses. Needle biopsy is safe and rapid. As the patient usually experiences only minimal discomfort and thereis no permanent scar, repeat biopsies are well tolerated allowing follow‐up studies after treatmen