Dodecacarbonyl-triruthenium and -triosmium react with thiols RSH to produce the trinuclear hydridocarbonyl complexes HM3(CO)10SR (M = Ru or Os; R = Et, Bun, or Ph.) These complexes are volatile, soluble in organic solvents, and are considered to be members of the series of compounds typified by HOs3(CO)10(OMe). N.m.r., i.r., and mass spectral data are reported and discussed in terms of cyclic, and hydrido- and thiol-bridged structures.