Reaction of Pt(S₂PPh₂)₂ with tertiary phosphines (PPh₃, PMePh₂, PMe₂Ph) gives crystalline 1 : 1 and 1 : 2 adducts. With triphenylarsine or triphenylstibine, only 1 : 1 adducts can be isolated and with pyridine, i.r. evidence indicates that the 1 : 1 adduct is only stable in solution in the presence of an excess of pyridine. As reported earlier for the analogous palladium compounds, the 1 : 2 adducts rapidly dissociate to the 1 : 1 compounds in non-polar solvents (benzene or carbon disulphide); however, it is now found that they can be stabilised in more polar solvents (dichloromethane or nitromethane). Conductivity measurements in the latter suggests all these 1 : 2 adducts have a four-co-ordinate ionic structure and this is confirmed by an X-ray analysis of [Pd(S₂PPh₂)(PEt₃)₂]S₂PPh₂. An X-ray analysis on [Pd(S₂PPh₂)₂(PPh₃)] suggests a four-co-ordinate monomeric structure for the 1 : 1 compounds with uni- and bi-dentate co-ordination of dithioacid ligands. Finally, an empirical i.r. method for distinguishing unidentate, bidentate, and ionic modes of co-ordination of the diphenylphosphinodithioato-group to platinum and palladium is discussed.