A new series of ligands is synthesised starting from thiocarbonohydrazide and isatin (H2itc) or N-alkylisatin (methyl, H2mtc; butyl, H2btc; pentyl, H2ptc); the X-ray structure of H2mtc is discussed. The bis imine ligands are reacted with diorganotin(IV) compounds, obtaining monometallic complexes. In order to establish unequivocally their coordination geometry, the X-ray structures of (C2H5)2Sn(Hmtc)Cl Æ THF (THF, tetrahydrofuran) and (C6H5)Sn(Hptc)Cl2 are determined. In (C2H5)2Sn(Hmtc)Cl Æ THF, the ligand results monodeprotonated and, essentially, monodentate through the sulphur atom, while in (C6H5)Sn(Hptc)Cl2 the ligand is still monodeprotonated but SNO tridentate. The organotin(IV) complexes of isatin and N-methylisatin exhibit good antibacterial activity, better than that of the corresponding N-butyl and N-pentylisatin derivatives. Gram positive bacteria are the most sensitive microorganisms. No growth inhibition of fungi is detected up to the concentration of 100 lg/ml. H2mtc shows mutagenic activity with and without metabolic activation, whereas no mutagenicity is found for its organotin complexes and for the other compounds.