The influence of oral zinc sulphate therapy on the humoral immunity was investigated by dosages of serum immunoglobulins (Ig) and of plasma zinc levels in 12 patients with a mean age of 70 years, in comparison with other 11 patients treated with placebo and with a control group of 50 apparently healthy subjects. The results of this double-blind study demonstrated the zinc effect on the immunoregulation, as the Ig levels, and particularly those of the IgG class, initially high, were lowered in a statistically significant proportion. It is assumed that further clinical trials with various zinc concentrations could bring more information on this trace element participation in the humoral immunoregulation.