Zinc concentrations in both serum and hair were assessed in 135 obese patients (51 males, 84 females) and in 57 controls (28 males, 29 females) to study the correlation between Zn and obesity. The body mass index (wt/ht2) was also measured to evaluate its relationship to the Zn level in obese individuals. The serum and hair Zn contents in obese patients were markedly lower than in normal control subjects by 22 and 34%, respectively. The Zn content was inversely related to the body mass index. Thus Zn may play an important metabolic role in the development of obesity.