A randomized, double blind crossover study of the effects of zinc sulfate and placebo was carried out in 106 patients with taste and smell dysfunction secondary to a variety of etiological factors. In the patient group prior to treatment, mean serum zinc concentration and leukocyte alkaline phosphatase activity were significantly lower than normal. Results indicate that zinc sulfate was effectively equivalent to placebo in the treatment of these disorders. Although these results demonstrate abnormalities of zinc metabolism in some patients with taste and smell dysfunction they fail to provide evidence for a single, therapeutic approach to the many disorders which are associated with abnormalities of taste and smell. However, the methods and procedures developed in this study demonstrate that taste and smell dysfunction can be studied in a quantitative, systematic manner.