A 61-year-old man developed clinical lupus syndrome with positive antinuclear antibody, positive lupus erythematosus (LE) cell preparation, and diffuse proliferative glomerulonephritis following 26 months of procainamide therapy. He was treated sequentially with prednisone and azathioprine (2 weeks), decreasing doses of prednisone alone (21 months), and no immunosuppressive drugs (10 months). Coincidental with this treatment, the immunopathology of the glomerulonephritis improved dramatically, dramatically, renal function returned almost to normal, and both antinuclear antibody and LE cell preparation became negative. The course of this patient's renal disease contrasts sharply with diffuse proliferative glomerulonephritis of idiopathic systemic lupus, and suggests that this rare complication of procainamide therapy may have a favorable course.