Complexes of thiazolidine-2-thione (ttz) were prepared and studied by magnetic techniques and u.v. visible, and i.r. spectroscopy. Pseudotetrahedral complexes [M(ttz)2X2] are formed with CoX2(X = Cl, Br, or I) and Nil2, while octahedral or distorted octahedral complexes [M(ttz)2X2] are formed with NiX2(X = Cl or Br). The ‘inner’ complex [Ni(C3H4NS2)2] has a distorted square-planar structure. It appears that this ligand co-ordinates through the sulphur heteroatom in tetrahedral complexes and through both sulphur atoms in octahedral ones.