Con A-induced capping of lymphocytes is altered by a number of cytoskeletal modulating agents. Zinc, in the presence of colchicine, demonstrated an age-dependent differential effect on con A-induced capping of human peripheral blood lymphocytes. In general, zinc enhanced capping of lymphocytes from young individuals and suppressed from those of old individuals. The effect of zinc on the cap formation adds further support to the evidence that zinc might be acting on the microfilaments. However, cytochalasin B, another microfilament modulating agent, does not show a differential effect similar to zinc. This suggests that zinc might modify microfilament formation or function in a manner different from cytochalasin B. The proposal that the effects of zinc might be due to its action on calmodulin suggests that calmodulin, the calcium regulating protein, may have a role in the physiological processes associated with aging. Further studies in this area might yield fruitful results in our understanding of the molecular mechanism of senescence.