A 43-year-old man with Eaton-Lambert syndrome developed chronic interstitial nephritis after 4 years of guanidine hydrochloride therapy. The diagnosis of Eaton-Lambert syndrome was confirmed by clinical neurophysiologic studies and by intracellular electrode studies of end-plate potentials from an intercostal muscle biopsy. Because guanidine had toxic effects in this patient, an alternative form of therapy was tried. Germine-3-acetate (500 mg per day orally) resulted in clinical and electric improvement of the myasthenic syndrome. However, the sensory side effects of numbness of the limbs and unpleasant taste were sufficiently annoying that germine was discontinued.