The stereoisomeric [1,2-bis(2-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) complexes were thoroughly tested on the cisplatin-resistant human NIH:OVCAR-3 ovarian cancer cell line. The racemate and its enantiomers produced cytocidal effects at a concentration of 2.5 microM (incubation time 256 h). The meso form, however, was merely cytostatically active. Differences between the enantiomers became evident after a short drug incubation time (1 h) followed by an incubation in drug-free medium (243 h). The S,S-configurated enantiomer (-)-3-PtCl2 proved to be the most active compound. To achieve cytocidal effects concentrations of 2.5-5.0 microM and incubation times of about 3 h were necessary for (-)-3-PtCl2. This compound is also sufficiently stable under test conditions as shown by the preincubation in cell-free medium for 3 h. These results and the augmentation of its antitumor activity by buthionine sulfoximine recommend the further preclinical development of (-)-3-PtCl2 for clinical use.