Résumé : The activity of stereoisomeric [1,2‐bis (3‐hydroxyphenyl)ethylenediamine]dichloroplatinum(II)‐complexes (1‐PtCl2, R, S; 2‐PtCl2, R, R/S, S; 3‐PtCl2, R, R; 4‐PtCl2, S, S) on several tumor models (MDA‐MB 231 breast cancer cell line; P 388 leukemia, mouse; L 1210 leukemia, mouse; L 5222 leukemia, rat; Ehrlich ascites tumor, mouse ‐ wildtype; cisplatin‐, etoposide‐, cyclophosphamide‐, and daunomycin‐resistent, resp.) is described. For comparison the analogous [1,2‐bis(4‐hydroxyphenyl)ethylendiamine]dichloroplatinum(II)‐complexes (5‐PtCl2, R, S; 6‐PtCl2, R, R/S, S; 7‐PtCl2, 8‐PtCl2, S, S) and cisplatin are used. 1‐PtCl2 to 4‐PtCl2 (OH in 3,3′‐positions) show their maximum antitumor effect at lower doses than 5‐PtCl2 to 8‐PtCl2 (OH in 4,4′‐positions). 2‐PtCl2 and 6‐PtCl2 (R, R/S, S) are more active than 1‐PtCl2 and 5‐PtCl2 (R, S). 4‐PtCl2 and 8‐PtCl2 (S, S) are superior to 3‐PtCl2 and 7‐PtCl2 S, S). On the L 5222 leukemia 2‐PtCl2 (R, R/S, S), 4‐PtCl2 (S, S) and 8‐PtCl2 (S, S) markedly surpass cisplatin. Strong effects are produced by 2‐PtCl2 to 4‐PtCl2 on the Ehrlich ascites tumor (wildtype, cisplatin‐, etoposide‐, cyclophosphamide‐, and daunomycin‐resistent, resp.). The combination of 4‐PtCl2 with cisplatin results in a weakly synergistic effect. Copyright © 1989 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim