Eleven patients with newly diagnosed Wilson's disease were treated with zinc acetate as their sole anticopper therapy. Treatment duration was 8 to 37 months. Three of the patients had symptoms; in eight who were presymptomatic, diagnosis was made because of affected siblings who had symptoms. All patients did well clinically. Copper absorption was suppressed, as reflected by blockade of absorption of orally administered copper 64. Values for 24-hour urine copper and nonceruloplasmin plasma copper (freely available copper) were reduced. Values for liver-derived serum enzymes were also generally reduced in patients who had pretreatment elevations. Percutaneous liver biopsies were done initially and repeated in seven of the patients after 12 to 35 months of zinc therapy. In five of these patients a second biopsy specimen showed higher levels of copper than the first. In three of these five a third biopsy 6 to 23 months after the second revealed liver copper values that either had returned to the baseline value or were lower. One patient's initial biopsy specimen showed active inflammation, which subsided with therapy. All of the biopsies revealed histologic scarring typical of cirrhosis, and this did not appear to change over the course of therapy. We conclude that hepatic copper may increase temporarily during early zinc therapy but that the accumulated copper is sequestered in a nontoxic form. On the basis of animal studies we postulate that this sequestered copper is primarily bound to the high levels of hepatic metallothionein induced by zinc. Zinc appears to be a reasonable option for the initial treatment of patients with Wilson's disease, particularly those with presymptomatic disease.