Primary membranous nephropathy is an autoimmune disease which demonstrates autoantibodies to the M-type phospholipase A2 receptor (PLA2R) in up to 70% of patients. Autoantibodies to PLA2R may be useful in distinguishing primary membranous nephropathy from secondary membranous nephropathy and other forms of glomerulonephritis. As such, testing for anti-PLA2R antibodies may be useful in patients with idiopathic nephrotic syndrome. In PLA2R antibody-positive patients, quantitative changes in the anti-PLA2R value generally precedes a change in clinical status with respect to clinical remission, relapse, or risk assessment after kidney transplantation.