SummaryA middle-aged woman had intermittently had ehloroquine as an antimalarial agent for 21 years. Although she had discontinued the drug for more than 10 years due to occurrence of a retinopathy, mild°cular myasthenic symptoms persisted. Cardiac induction disturbances were detected as well. A quadriceps muscle biopsy revealed mild neurogenic changes and interstitial lymphorrhages. The decremental response after repetitive stimulation was reversed by edrophonium administration. The history Suggests that the persisting myasthenia might have keen caused by ehloroquine intake.