Zinc is an important trace element for immune function. Here, we show that zinc addition in a serum- and lipopolysaccharide-free cell culture system leads to significantly enhanced levels of interleukin 1 beta (IL-1 beta) and tumour necrosis factor alpha (TNF-alpha) and to expression of the corresponding mRNA in human peripheral blood mononuclear cells (PBMC). Structurally related divalent cations like cobalt, nickel, and mercury also partially increase monokine secretion but to a much lower and thus insignificant extent. They fail to induce mRNA of TNF-alpha after 3 h of culture. Therefore, monokine induction is a zinc-specific effect influenced by the physicochemical properties of the ion. Confirmation of the unique significance of zinc for immune function provides a better understanding of the mechanisms of specific zinc-mediated immune modulation.