The molybdenum nitrido-complexes [MoN(S2CNR2)3] react with elemental sulphur or propylene sulphide to give the thionitrosyl complexes [Mo(NS)(S2CNR2)3] in high yield. The rhenium nitrido-complexes [ReX2N(PR3)3](PR3= PMe2Ph, PEt2Ph, or PMePh2; X = Cl or Br) react with half an equivalent of S2Cl2 to give the pink thionitrosyl complexes [ReCl(X)(NS)(PR3)3] in yields of 60–70%. Use of an excess of S2Cl2 gives the purple complexes [ReCl2X(NS)(PR3)2] in good yields. The five-co-ordinate nitrido-complexes [ReCl2N(PRPh2)2](R = Ph or Prn) also give [ReCl3(NS)(PRPh2)2] on reaction with half an equivalent of S2Cl2. The osmium nitrido-complexes [OsX3NL2][L = AsPh3, PMe2Ph, ½ bipy (2,2′-bipyridyl), or py (pyridine); X = Cl or Br] react analogously with S2Cl2 to give [OsClX2(NS)L2]. ν(N–S) appears in the i.r. spectra in the range 1 120–1 280 cm–1, and the 1H n.m.r. spectra of the diamagnetic complexes show the phosphines to be mer in [ReCl2(NS)(PR3)3] and trans in [OsCl3(NS)(PMe2Ph)2]. Treatment of the thionitrosyls with tertiary phosphines regenerates the parent nitrido-complexes in high yields.