Triethylene tetramine (trien), in increasing dose from 1.0-2.0 g/day to 2.5-3.0 g/day, was used for 4 Japanese patients with Wilson's disease who were intolerant of D-penicillamine (D-PC). Before the treatment, urinary copper excretion (UCE) was 70-96 micrograms/day. UCE increased to 1,512-2,352 micrograms/day on the day of initial administration, and remained at levels between 350-1,100 micrograms/day, thereafter. During 2 months of trien therapy, neurological deficits regressed in three patients, and only slightly in one patient. No adverse effects were observed. These results and the retrospective survey on 17 patients treated with D-PC confirmed that trien is less potent but a safer copper chelating agent than D-PC. The transient aggravation of neurological deficits seen in two patients during the early stage of the treatment suggested that trien, as D-PC, should be started in small doses and gradually increased.