INVESTIGATIONS of metal alkoxides1 have shown that polymeric molecules [M(OR)x]n are generally formed unless the alkyl group (R) is bulky. Work on sulphur analogues known as metal mercaptides M(SR)x was undertaken in order to compare the structures and properties of metal alkoxides and metal mercaptides. A survey of the work on metal mercaptides showed that the lowest mercaptide, mercury methyl mercaptide Hg(S.CH3)2, has quite a compact structure2 having weak intermolecular Hg-S bonds. The structure is consistent with the high melting point (185°) and low solubility of this compound. The next higher mercaptide, mercury ethyl mercaptide Hg(S.Et)2, melts at a low temperature (76°) and as such has essentially a molecular structure3. The structures of most of the higher mercaptides are likely to be molecular since they are volatile and soluble in organic solvents. The properties of mercury tert-butyl mercaptide did not fit into this pattern. This compound has a low solubility and sublimes at a high temperature (135°) under low pressure. An X-ray analysis of this compound was, therefore, undertaken in order to elucidate its crystal structure.