Abstract The preparation and i.r. spectra of some bidentate thiosulphato complexes of palladium(II) are reported. The complex K 2[Pd(S 2O 3] 2] exists both as an insoluble form and also as a soluble modification. The insoluble form is believed to involve catena-di-μ-thiosulphatopalladate(II) anions, whereas the soluble form probably contains chelating sulphato groups co-ordinated through one oxygen atom and one sulphur atom. The complex PdS 2O 31·5 en ( en = ethylenediamine), previously formulated as [Pd en(S 2)O 3)]·2H 2O, can be correctly viewed as [Pd( en) 2][Pd en(S 2O 3) 2]. The reaction of [Pd(NH 3) 4] 2+ with S 2O 3 2− leads to the formation of the following compounds: Na 2[Pd(S 2O 3) 2]·H 2O, PdS 2O 3·2NH 3, Pd(NH 3) 3S 2O 3 and [Pd(NH 3) 4][Pd(NH 3) 2(S 2O 3) 2]; the first two compounds probably involve bridging thiosulphato groups.