Because procainamide hydrochloride (Pronestyl) may block neuromuscular transmission (NMT), this drug is contraindicated in cases of myasthenia gravis. Reduction of the safety factor of NMT is also seen in other conditions, including peripheral neuropathies. A patient with uremic peripheral neuropathy in whom myasthenia-like weakness developed during procainamide therapy is described. Procainamide should be given with caution in cases of peripheral neuropathies in which there may be a reduction of the safety factor of NMT.