The role of zinc in some metabolic functions in man was investigated in 14 healthy male volunteers with primarily high or low serum zinc. In all the subjects, results of laboratory tests reflecting blood picture, metabolism of carbohydrates, fats and proteins and thyroid function as well as serum calcium and phosphate levels varied within the normal range. Significant differences between the subjects classified by serum zinc were found in α1-globulins. Serum thyroxine, effective thyroxine ratio and the immunoglobulins IgA showed a tendency to lower levels in subjects with low serum zinc. Substitution with zinc sulphate resulted in an increase of α1 -globulins, serum thyroxine and effective thyroxine ratio, and a decrease of albumin. Other tests remained unchanged by the therapy. The results suggest that there is a relationship between zinc and some metabolic functions in healthy subjects without symptoms of zinc deficiency.