To evaluate zinc status in Alzheimer's disease and Parkinson's disease, 29 patients with Alzheimer's disease, 30 patients with Parkinson's disease, and 29 age- and sex-matched controls were studied. All patients and controls were older than age 50, and all zinc and copper supplements were prohibited beginning 30 days prior to study. Patients were diagnosed by standard criteria. Blood zinc and urine zinc were measured. Urine zinc was measured in a casual specimen, standardized for dilution by reference to creatinine content. Results showed a significantly lower blood zinc in patients with Alzheimer's and patients with Parkinson's than in controls. Urine zinc excretion, normalized to urine creatinine excretion, was not significantly different in either patient group compared to controls. These patients are probably zinc deficient because of nutritional inadequacy.