Nickel, copper, and zinc complexes of isatin (H(2)L(1)) and N-methylisatin 3-picolinoyl hydrazone (HL(2)), were synthesized and characterized by means of spectroscopic techniques. H(2)L(1) and a nickel complex [Ni(L(2))(2)].2C(6)H(14) were also characterized by X-ray diffractometry. Biological studies, carried out in vitro on human leukemic cell lines TOM 1 and NB4, have shown that both ligands and some copper and nickel complexes are active in inhibiting cell proliferation. Compounds H(2)L(1), Cu(HL(1))(2).2H(2)O, Zn(HL(1))(2).2H(2)O inhibit DNA synthesis and act constantly with time between 0 and 72 h. The cell cycle analysis has highlighted a reduction in the number of cells in phase S of about 40%. The same compounds present only a precocious action on cell line NB4 and therefore their activity is cell target specific.