Immunoglobulin light chain amyloidosis and the kidney. Amyloidosis (AL) is a common cause of nephrotic syndrome in nondiabetic, nonhypertensive adults. All adult patients with nephrotic syndrome should have immunofixation of serum and urine as a screen. The finding of a monoclonal protein, particularly of lambda type, should lead to a subcutaneous fat aspirate or bone marrow biopsy to search for amyloid deposits. When the result of either test is positive, a kidney biopsy is unnecessary. The prognosis of patients who have renal amyloidosis depends on the concentration of serum creatinine at presentation and whether an echocardiographic evaluation demonstrates infiltrative cardiomyopathy. Most therapies are directed against the plasma cell dyscrasia present in all patients with AL and can include melphalan and prednisone, high-dose dexamethasone, and, most recently, peripheral blood stem cell transplantation.