Ninety-nine patients were treated with hydroxychloroquine sulfate for connective tissue diseases during a seven year period. All patients received the medication for at least one year and most were treated with a daily dosage of 400 mg. Four patients experienced toxic effects, but no patient sustained permanent loss of visual acuity. Toxicity did not seem to represent a cumulative dosage effect. Funduscopic and visual field examinations at six-month intervals are sufficient to detect the occasional adverse reactions and prevent serious retinal toxic effects when a maximum daily dosage of 400 mg is maintained.