Techniques of percutaneous synovial biopsy under fluoroscopic control of large joints of the limbs (other than the knee) may be useful in arthritis of undetermined etiology especially when infection is considered. Main technical refinements include adequate selection of an optimal approach and biopsy site using new imaging methods, use of a Tru-Cut(R) needle, and placement of the cutting window tangential to the joint surface, and selection of an optimal approach and biopsy site. Detailed technique of the synovial biopsy of hip, ankle, shoulder, and elbow joints is discussed.