Sporadic late onset nemaline myopathy (SLONM) is a progressive myopathy of indeterminate etiology and poor outcome. If associated with a monoclonal gammopathy, SLONM carries a more unfavorable prognosis. Immunotherapy was unsuccessful. We report two HIV-negative SLONM/monoclonal gammopathy patients who improved following intravenous immunoglobulin (IVIg) treatment alone or in combination with immunosuppressant agents. This favorable response to treatment suggests that a dysimmune mechanism is operative in some SLONM individuals. We suggest that IVIg deserves initial consideration for SLONM therapy.