Reduced food consumption is a major manifestation of zinc (Zn) deficiency. Many manifestations of Zn deficiency are complications of anorexia nervosa and bulimia nervosa. We evaluated serum and 24-hour urinary Zn values in 12 healthy volunteers and 33 eating disorder patients before and after hospitalization which included either Zn supplementation (75 mg Zn/day) or placebo. Bulimics had depressed serum Zn concentrations (p < 0.025). Admission urinary Zn was lower in bulimics (258 +/- 44 micrograms/day), and significantly depressed in anorexics (196 +/- 36 micrograms/day, p < 0.005) vs controls (376 +/- 45 micrograms/day). During hospitalization, serum Zn concentrations increased in all supplemented patients vs no change with placebo. Urinary Zn excretion increased in supplemented bulimics (p < 0.001) and placebo (p < 0.05). Urinary Zn excretion markedly increased in supplemented anorexics (179 +/- 65 to 1052 +/- 242 micrograms/day); however, placebo values fell or remained unacceptably low (admission 208 +/- 48 micrograms/day; discharge 160 +/- 17 micrograms/day). By dietary history, controls consumed the Recommended Dietary Allowance (RDA) for Zn (11.95 +/- 1.25 mg/day); anorexics 6.46 +/- 1.14 mg/day; and bulimics 8.93 +/- 1.29 mg/day. We suggest that Zn deficiency may act as a "sustaining" factor for abnormal eating behavior in certain eating disorder patients.