The degree of chromosome damage induced by three compounds of zinc (zinc chloride, zinc sulfate, zinc acetate) was compared in human leucocytes in vitro. Three concentrations of each salt, 3.0 × 10-5M, 3.0 × 10-4M, and 1.5 × 10-3M, were added to leukocyte cultures. The cells were harvested after 48 and 72 h and chromosome spreads were prepared following a colchicine-hypotonic-fixation-air drying-Giemsa staining schedule. The end point screened was chromosome aberrations. All three salts were lethal at the highest concentration. The degree of chromosome damage was directly proportional to the concentrations used for zinc sulfate and zinc acetate but not for zinc chloride.