The interaction of hydrogen sulphide,n-propyl mercaptan, and dimethyl disulphide with the (111) and (100) faces of nickel has been studied by LEED at temperatures up to 700 K. During interaction and subsequent annealing,in vacuobelow10−9 Torrat temperatures up to 1200 K, series of diffraction patterns were observed. Four of the patterns on (111) have been attributed to coincidence nets arising from structures which involve rearrangement and reorientation to (100) type layers. The patterns are described and the interpretations discussed.