In order to study the chelating action of d-penicillamine on lead and the possibility of its application to the provocation test for diagnosis of lead poisoning, urinary excretion of lead was measured from 24-hour urine samples before, during and after administration of d-penicillamine by oral route for 5 days on 18 lead workers. The results were as follows: 1. Oral d-penicillamine 600 mg/day raised the excretion of urinary lead by approximately 3 times as compared with initial urinary lead level. 2. Initial urinary lead level was the better indicator of urinary lead excretion in d-penicillamine administration than initial blood lead ${delta}-ALA$ and hemoglobin level. 3. Oral d-penicillamine may be quite useful in provocation test for lead poisoning.