Résumé : The antitumor activities of three novel condensation products of salicylaldoxime with di‐n‐butyltin(IV) oxide (compound 1), di‐t‐butyltin oxide (compound 2) and diphenyltin oxide (compound 3) are presented. Against MCF‐7, a human mammary tumor cell line, compounds 1 and 2 are characterized by inhibition doses ID50 in vitro of 67 and 49 ng cm−3 respectively, whereas cis‐platin, an antitumor drug used clinically, has an ID50 of 850 ng cm−3. Against WiDr, a colon carcinoma, they also score better than cis‐platin: 215 and 121 ng cm−3 versus 624 ng cm−3. In contrast, the diphenyltin compound, 3, is inactive against both tumor cell lines. The results of a pre‐screening performed on compound 1 by the National Cancer Institute (NCI) on a panel of 60 human tumor cell lines show that two of the selectivity parameters calculated by the NCI for that compound are statistically significant, namely DG150 (51.9>50) and MGDH (80.1>75). One is almost satisfactory (DH = 72.4 = ca75). The other two, DTGI (40.0<50) and DLC50 (16.7<50) are not. (Abbreviations are explained in the text and in Gielen, M. and Willem, R. Anticancer Res., 1992, in press). Copyright © 1992 John Wiley & Sons Ltd.