Résumé : The X-ray crystal structures of [diethyl(2-methylthio-3-pyridinecarboxylato)tin] oxide (1a) and diethyltin bis(2-methylthio-3-pyridinecarboxylate) (1b) were determined. Compound 1a is a centrosymmetric dimer with two distinct types of carboxylate moieties and tin atoms with trigonal bipyramidal geometries. Compound 1b is monomeric with a six-coordinate tin atom and two equivalent carboxylate groups chelating the tin atom. Compounds 2a and 2b, the di-n-butyl analogues of 1a and 1b, have also been synthesized and characterized spectroscopically. The in vitro activity of compounds 2b and 2a against the human tumour cell line WiDr, a colon carcinoma, is better than that of cis-platin and doxorubicin. They are much less active than doxorubicin against MCF-7, a mammary tumour cell line. Compound 1b is inactive. © 1992.