2,3-Dimercaptosuccinic acid (D.M.S.), a new orally effective agent for the treatment of heavy-metal intoxication, was administered to five lead-poisoned smelter workers for six days at dosages ranging from 8.4--12.7 mg/kg/day on the first day to 28.1--42.2 mg/kg/day on the last day. Mean blood-lead concentration decreased significantly from an initial value of 97 +/- 6 microgram/dl to 43 +/- 4 microgram/dl on the last day. Urinary lead excretion was significantly raised. D.M.S. was very well tolerated with no signs of toxicity and no effect on urinary zinc, calcium, magnesium, or iron excretion. Urinary copper excretion was significantly increased, but the magnitude of that effect was not clinically important. D.M.S. seems to be safe and effective for the treatment of lead poisoning.